diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f02e2e9..e705fe1 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -2,10 +2,10 @@ name: Test
 on:
   push:
     branches:
-      - 2.x
+      - 3.x
   pull_request:
     branches:
-      - 2.x
+      - 3.x
 
 jobs:
   test:
@@ -18,10 +18,10 @@ jobs:
       fail-fast: false
       matrix:
         php-version:
-          - "7.2"
-          - "7.3"
           - "7.4"
           - "8.0"
+          - "8.1"
+          - "8.2"
         composer-version:
           - "2"
     steps:
diff --git a/composer.json b/composer.json
index 4d7f19d..1b3c25d 100644
--- a/composer.json
+++ b/composer.json
@@ -4,7 +4,8 @@
     "type": "library",
     "keywords": ["payment"],
     "require": {
-        "php": "^7.2 || ^8.0",
+        "php": "^7.4 || ^8.0",
+        "ext-json": "*",
         "psr/http-message": "^1.0",
         "psr/http-client-implementation": "^1.0",
         "php-http/message": "^1.6",
diff --git a/phpstan.neon b/phpstan.neon
index 167c6f1..3dcf784 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -4,6 +4,12 @@ parameters:
         - src
         - test
     ignoreErrors:
+        # Ignore Call to an undefined static method zaporylie\Vipps\Resource\HttpMethod::POST().
+        - '#Call to an undefined static method zaporylie\\Vipps\\Resource\\HttpMethod::POST\(\)#'
+        - '#Call to an undefined static method zaporylie\\Vipps\\Resource\\HttpMethod::PUT\(\)#'
+        - '#Call to an undefined static method zaporylie\\Vipps\\Resource\\HttpMethod::PATCH\(\)#'
+        - '#Call to an undefined static method zaporylie\\Vipps\\Resource\\HttpMethod::DELETE\(\)#'
+        - '#Call to an undefined static method zaporylie\\Vipps\\Resource\\HttpMethod::GET\(\)#'
 
 includes:
 	- phpstan-baseline.neon
diff --git a/src/Api/ApiBase.php b/src/Api/ApiBase.php
index 9fa06dc..788171f 100644
--- a/src/Api/ApiBase.php
+++ b/src/Api/ApiBase.php
@@ -11,12 +11,12 @@ abstract class ApiBase
     /**
      * @var \zaporylie\Vipps\VippsInterface
      */
-    protected $app;
+    protected VippsInterface $app;
 
     /**
      * @var string
      */
-    protected $subscriptionKey;
+    protected string $subscriptionKey;
 
     /**
      * ApiBase constructor.
@@ -24,7 +24,7 @@ abstract class ApiBase
      * @param \zaporylie\Vipps\VippsInterface $app
      * @param string $subscription_key
      */
-    public function __construct(VippsInterface $app, $subscription_key)
+    public function __construct(VippsInterface $app, string $subscription_key)
     {
         $this->app = $app;
         $this->subscriptionKey = $subscription_key;
@@ -35,7 +35,7 @@ public function __construct(VippsInterface $app, $subscription_key)
      *
      * @return string
      */
-    public function getSubscriptionKey()
+    public function getSubscriptionKey(): string
     {
         if (empty($this->subscriptionKey)) {
             throw new InvalidArgumentException('Missing subscription key');
@@ -50,7 +50,7 @@ public function getSubscriptionKey()
      *
      * @return $this
      */
-    public function setSubscriptionKey($subscriptionKey)
+    public function setSubscriptionKey(string $subscriptionKey): self
     {
         $this->subscriptionKey = $subscriptionKey;
         return $this;
diff --git a/src/Api/Authorization.php b/src/Api/Authorization.php
index 002b42b..a0b39d9 100644
--- a/src/Api/Authorization.php
+++ b/src/Api/Authorization.php
@@ -2,6 +2,7 @@
 
 namespace zaporylie\Vipps\Api;
 
+use zaporylie\Vipps\Model\Authorization\ResponseGetToken;
 use zaporylie\Vipps\Resource\Authorization\GetToken;
 
 class Authorization extends ApiBase implements AuthorizationInterface
@@ -9,10 +10,8 @@ class Authorization extends ApiBase implements AuthorizationInterface
 
     /**
      * {@inheritdoc}
-     *
-     * @return \zaporylie\Vipps\Model\Authorization\ResponseGetToken
      */
-    public function getToken($client_secret)
+    public function getToken($client_secret): ResponseGetToken
     {
         // Initiate GetToken resource.
         $resource = new GetToken($this->app, $this->getSubscriptionKey(), $client_secret);
diff --git a/src/Api/AuthorizationInterface.php b/src/Api/AuthorizationInterface.php
index 91ad5d8..c9abdc7 100644
--- a/src/Api/AuthorizationInterface.php
+++ b/src/Api/AuthorizationInterface.php
@@ -8,6 +8,8 @@
 
 namespace zaporylie\Vipps\Api;
 
+use zaporylie\Vipps\Model\Authorization\ResponseGetToken;
+
 interface AuthorizationInterface
 {
 
@@ -16,5 +18,5 @@ interface AuthorizationInterface
      *
      * @return \zaporylie\Vipps\Model\Authorization\ResponseGetToken
      */
-    public function getToken($client_secret);
+    public function getToken(string $client_secret): ResponseGetToken;
 }
diff --git a/src/Api/Payment.php b/src/Api/Payment.php
index d9b791f..ab622fa 100644
--- a/src/Api/Payment.php
+++ b/src/Api/Payment.php
@@ -2,6 +2,7 @@
 
 namespace zaporylie\Vipps\Api;
 
+use http\Env\Response;
 use zaporylie\Vipps\Exceptions\Api\InvalidArgumentException;
 use zaporylie\Vipps\Model\Payment\CustomerInfo;
 use zaporylie\Vipps\Model\Payment\MerchantInfo;
@@ -9,6 +10,12 @@
 use zaporylie\Vipps\Model\Payment\RequestCapturePayment;
 use zaporylie\Vipps\Model\Payment\RequestInitiatePayment;
 use zaporylie\Vipps\Model\Payment\RequestRefundPayment;
+use zaporylie\Vipps\Model\Payment\ResponseCancelPayment;
+use zaporylie\Vipps\Model\Payment\ResponseCapturePayment;
+use zaporylie\Vipps\Model\Payment\ResponseGetOrderStatus;
+use zaporylie\Vipps\Model\Payment\ResponseGetPaymentDetails;
+use zaporylie\Vipps\Model\Payment\ResponseInitiatePayment;
+use zaporylie\Vipps\Model\Payment\ResponseRefundPayment;
 use zaporylie\Vipps\Model\Payment\Transaction;
 use zaporylie\Vipps\Resource\Payment\CancelPayment;
 use zaporylie\Vipps\Resource\Payment\CapturePayment;
@@ -29,19 +36,19 @@ class Payment extends ApiBase implements PaymentInterface
     /**
      * @var string
      */
-    protected $merchantSerialNumber;
+    protected string $merchantSerialNumber;
 
     /**
      * @var string
      */
-    protected $customPath;
+    protected string $customPath;
 
     /**
      * Gets merchantSerialNumber value.
      *
      * @return string
      */
-    public function getMerchantSerialNumber()
+    public function getMerchantSerialNumber(): string
     {
         if (empty($this->merchantSerialNumber)) {
             throw new InvalidArgumentException('Missing merchant serial number');
@@ -52,7 +59,7 @@ public function getMerchantSerialNumber()
     /**
      * @return string
      */
-    public function getCustomPath()
+    public function getCustomPath(): string
     {
         return $this->customPath;
     }
@@ -69,9 +76,9 @@ public function getCustomPath()
      */
     public function __construct(
         VippsInterface $app,
-        $subscription_key,
-        $merchant_serial_number,
-        $custom_path = 'ecomm'
+        string $subscription_key,
+        string $merchant_serial_number,
+        string $custom_path = 'ecomm'
     ) {
         parent::__construct($app, $subscription_key);
         $this->merchantSerialNumber = $merchant_serial_number;
@@ -81,7 +88,7 @@ public function __construct(
     /**
      * {@inheritdoc}
      */
-    public function cancelPayment($order_id, $text)
+    public function cancelPayment(string $order_id, string $text): ResponseCancelPayment
     {
         // Build request object from data passed to method.
         $request = (new RequestCancelPayment())
@@ -103,7 +110,7 @@ public function cancelPayment($order_id, $text)
     /**
      * {@inheritdoc}
      */
-    public function capturePayment($order_id, $text, $amount = 0)
+    public function capturePayment(string $order_id, string $text, int $amount = 0): ResponseCapturePayment
     {
         // Build request object from data passed to method.
         $request = (new RequestCapturePayment())
@@ -129,7 +136,7 @@ public function capturePayment($order_id, $text, $amount = 0)
     /**
      * {@inheritdoc}
      */
-    public function getOrderStatus($order_id)
+    public function getOrderStatus(string $order_id): ResponseGetOrderStatus
     {
         // Get order status.
         // this is GET request so no need to create request object.
@@ -147,7 +154,7 @@ public function getOrderStatus($order_id)
     /**
      * {@inheritdoc}
      */
-    public function getPaymentDetails($order_id)
+    public function getPaymentDetails(string $order_id): ResponseGetPaymentDetails
     {
         // Get payment details.
         // this is GET request so no need to create request object.
@@ -166,13 +173,13 @@ public function getPaymentDetails($order_id)
      * {@inheritdoc}
      */
     public function initiatePayment(
-        $order_id,
-        $amount,
-        $text,
-        $callbackPrefix,
-        $fallback,
-        $options = []
-    ) {
+        string $order_id,
+        int $amount,
+        string $text,
+        string $callbackPrefix,
+        string $fallback,
+        array $options = []
+    ): ResponseInitiatePayment {
         // Create Request object based on data passed to this method.
         $request = (new RequestInitiatePayment())
             ->setCustomerInfo(
@@ -232,7 +239,7 @@ public function initiatePayment(
     /**
      * {@inheritdoc}
      */
-    public function refundPayment($order_id, $text, $amount = 0)
+    public function refundPayment(string $order_id, string $text, int $amount = 0): ResponseRefundPayment
     {
         // Prepare request object based on data passed to method.
         $request = (new RequestRefundPayment())
diff --git a/src/Api/PaymentInterface.php b/src/Api/PaymentInterface.php
index c53c71e..9fdeb07 100644
--- a/src/Api/PaymentInterface.php
+++ b/src/Api/PaymentInterface.php
@@ -2,6 +2,13 @@
 
 namespace zaporylie\Vipps\Api;
 
+use zaporylie\Vipps\Model\Payment\ResponseCancelPayment;
+use zaporylie\Vipps\Model\Payment\ResponseCapturePayment;
+use zaporylie\Vipps\Model\Payment\ResponseGetOrderStatus;
+use zaporylie\Vipps\Model\Payment\ResponseGetPaymentDetails;
+use zaporylie\Vipps\Model\Payment\ResponseInitiatePayment;
+use zaporylie\Vipps\Model\Payment\ResponseRefundPayment;
+
 /**
  * Interface PaymentInterface
  *
@@ -16,7 +23,7 @@ interface PaymentInterface
      *
      * @return \zaporylie\Vipps\Model\Payment\ResponseCancelPayment
      */
-    public function cancelPayment($order_id, $text);
+    public function cancelPayment(string $order_id, string $text): ResponseCancelPayment;
 
     /**
      * @param string $order_id
@@ -25,7 +32,7 @@ public function cancelPayment($order_id, $text);
      *
      * @return \zaporylie\Vipps\Model\Payment\ResponseCapturePayment
      */
-    public function capturePayment($order_id, $text, $amount = 0);
+    public function capturePayment(string $order_id, string $text, int $amount = 0): ResponseCapturePayment;
 
     /**
      * @param string $order_id
@@ -35,14 +42,14 @@ public function capturePayment($order_id, $text, $amount = 0);
      * @deprecated Get order status was deprecated and can be removed in version 3.0.
      * @see \zaporylie\Vipps\Resource\Payment\GetOrderStatus
      */
-    public function getOrderStatus($order_id);
+    public function getOrderStatus(string $order_id): ResponseGetOrderStatus;
 
     /**
      * @param string $order_id
      *
      * @return \zaporylie\Vipps\Model\Payment\ResponseGetPaymentDetails
      */
-    public function getPaymentDetails($order_id);
+    public function getPaymentDetails(string $order_id): ResponseGetPaymentDetails;
 
     /**
      * @param string $order_id
@@ -50,14 +57,14 @@ public function getPaymentDetails($order_id);
      * @param string $text
      * @param string $callbackPrefix
      * @param string $fallback
-     * @param $options array
+     * @param array $options
      *   Optional values.
      *
      * @return \zaporylie\Vipps\Model\Payment\ResponseInitiatePayment
      *
      * @see https://vippsas.github.io/vipps-ecom-api/#/Vipps_eCom_API/initiatePaymentV3UsingPOST
      */
-    public function initiatePayment($order_id, $amount, $text, $callbackPrefix, $fallback, $options = []);
+    public function initiatePayment(string $order_id, int $amount, string $text, string $callbackPrefix, string $fallback, array $options = []): ResponseInitiatePayment;
 
     /**
      * @param string $order_id
@@ -66,5 +73,5 @@ public function initiatePayment($order_id, $amount, $text, $callbackPrefix, $fal
      *
      * @return \zaporylie\Vipps\Model\Payment\ResponseRefundPayment
      */
-    public function refundPayment($order_id, $text, $amount = 0);
+    public function refundPayment(string $order_id, string $text, int $amount = 0): ResponseRefundPayment;
 }
diff --git a/src/Api/RecurringPayment.php b/src/Api/RecurringPayment.php
index 51d98b5..ef3528e 100644
--- a/src/Api/RecurringPayment.php
+++ b/src/Api/RecurringPayment.php
@@ -3,10 +3,15 @@
 namespace zaporylie\Vipps\Api;
 
 use zaporylie\Vipps\Exceptions\Api\InvalidArgumentException;
+use zaporylie\Vipps\Model\RecurringPayment\Charge;
 use zaporylie\Vipps\Model\RecurringPayment\RequestCreateAgreement;
 use zaporylie\Vipps\Model\RecurringPayment\RequestCreateCharge;
 use zaporylie\Vipps\Model\RecurringPayment\RequestRefundCharge;
 use zaporylie\Vipps\Model\RecurringPayment\RequestUpdateAgreement;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseCreateAgreement;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseCreateCharge;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseGetAgreement;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseUpdateAgreement;
 use zaporylie\Vipps\Resource\RecurringPayment\CancelCharge;
 use zaporylie\Vipps\Resource\RecurringPayment\CaptureCharge;
 use zaporylie\Vipps\Resource\RecurringPayment\CreateAgreement;
@@ -52,13 +57,13 @@ public function getMerchantSerialNumber()
      *
      * @param \zaporylie\Vipps\VippsInterface $app
      * @param string $subscription_key
-     * @param $merchant_serial_number
-     * @param $custom_path
+     * @param string $merchant_serial_number
+     * @param string $custom_path
      */
     public function __construct(
         VippsInterface $app,
-        $subscription_key,
-        $merchant_serial_number
+        string $subscription_key,
+        string $merchant_serial_number
     ) {
         parent::__construct($app, $subscription_key);
         $this->merchantSerialNumber = $merchant_serial_number;
@@ -67,7 +72,7 @@ public function __construct(
     /**
      * {@inheritdoc}
      */
-    public function createAgreement(RequestCreateAgreement $request)
+    public function createAgreement(RequestCreateAgreement $request): ResponseCreateAgreement
     {
         $resource = new CreateAgreement($this->app, $this->getSubscriptionKey(), $request);
         $response = $resource->call();
@@ -77,7 +82,7 @@ public function createAgreement(RequestCreateAgreement $request)
     /**
      * {@inheritdoc}
      */
-    public function getAgreements()
+    public function getAgreements(): array
     {
         $resource = new GetAgreements($this->app, $this->getSubscriptionKey());
         $response = $resource->call();
@@ -87,7 +92,7 @@ public function getAgreements()
     /**
      * {@inheritdoc}
      */
-    public function getAgreement($agreement_id)
+    public function getAgreement(string $agreement_id): ResponseGetAgreement
     {
         $resource = new GetAgreement($this->app, $this->getSubscriptionKey(), $agreement_id);
         $response = $resource->call();
@@ -97,7 +102,7 @@ public function getAgreement($agreement_id)
     /**
      * {@inheritdoc}
      */
-    public function updateAgreement($agreement_id, RequestUpdateAgreement $request)
+    public function updateAgreement(string $agreement_id, RequestUpdateAgreement $request): ResponseUpdateAgreement
     {
         $resource = new UpdateAgreement($this->app, $this->getSubscriptionKey(), $agreement_id, $request);
         $response = $resource->call();
@@ -107,7 +112,7 @@ public function updateAgreement($agreement_id, RequestUpdateAgreement $request)
     /**
      * {@inheritDoc}
      */
-    public function getCharges($agreement_id)
+    public function getCharges(string $agreement_id): array
     {
         $resource = new GetCharges($this->app, $this->getSubscriptionKey(), $agreement_id);
         $response = $resource->call();
@@ -117,7 +122,7 @@ public function getCharges($agreement_id)
     /**
      * {@inheritDoc}
      */
-    public function getCharge($agreement_id, $charge_id)
+    public function getCharge(string $agreement_id, $charge_id): Charge
     {
         $resource = new GetCharge($this->app, $this->getSubscriptionKey(), $agreement_id, $charge_id);
         $response = $resource->call();
@@ -127,7 +132,7 @@ public function getCharge($agreement_id, $charge_id)
     /**
      * {@inheritDoc}
      */
-    public function createCharge($agreement_id, RequestCreateCharge $request)
+    public function createCharge(string $agreement_id, RequestCreateCharge $request): ResponseCreateCharge
     {
         $resource = new CreateCharge($this->app, $this->getSubscriptionKey(), $agreement_id, $request);
         $response = $resource->call();
@@ -137,7 +142,7 @@ public function createCharge($agreement_id, RequestCreateCharge $request)
     /**
      * {@inheritDoc}
      */
-    public function cancelCharge($agreement_id, $charge_id)
+    public function cancelCharge($agreement_id, $charge_id): string
     {
         $resource = new CancelCharge($this->app, $this->getSubscriptionKey(), $agreement_id, $charge_id);
         $response = $resource->call();
@@ -147,7 +152,7 @@ public function cancelCharge($agreement_id, $charge_id)
     /**
      * {@inheritDoc}
      */
-    public function captureCharge($agreement_id, $charge_id)
+    public function captureCharge($agreement_id, $charge_id): string
     {
         $resource = new CaptureCharge($this->app, $this->getSubscriptionKey(), $agreement_id, $charge_id);
         $response = $resource->call();
@@ -157,7 +162,7 @@ public function captureCharge($agreement_id, $charge_id)
     /**
      * {@inheritDoc}
      */
-    public function refundCharge($agreement_id, $charge_id, RequestRefundCharge $requestObject)
+    public function refundCharge($agreement_id, $charge_id, RequestRefundCharge $requestObject): string
     {
         $resource = new RefundCharge(
             $this->app,
diff --git a/src/Api/RecurringPaymentInterface.php b/src/Api/RecurringPaymentInterface.php
index 2f582ad..76317d5 100644
--- a/src/Api/RecurringPaymentInterface.php
+++ b/src/Api/RecurringPaymentInterface.php
@@ -2,10 +2,15 @@
 
 namespace zaporylie\Vipps\Api;
 
+use zaporylie\Vipps\Model\RecurringPayment\Charge;
 use zaporylie\Vipps\Model\RecurringPayment\RequestCreateAgreement;
 use zaporylie\Vipps\Model\RecurringPayment\RequestCreateCharge;
 use zaporylie\Vipps\Model\RecurringPayment\RequestRefundCharge;
 use zaporylie\Vipps\Model\RecurringPayment\RequestUpdateAgreement;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseCreateAgreement;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseCreateCharge;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseGetAgreement;
+use zaporylie\Vipps\Model\RecurringPayment\ResponseUpdateAgreement;
 
 /**
  * Interface PaymentInterface
@@ -20,17 +25,17 @@ interface RecurringPaymentInterface
      *
      * @return \zaporylie\Vipps\Model\RecurringPayment\ResponseCreateAgreement
      */
-    public function createAgreement(RequestCreateAgreement $requestCreateAgreement);
+    public function createAgreement(RequestCreateAgreement $requestCreateAgreement): ResponseCreateAgreement;
 
     /**
      * @return \zaporylie\Vipps\Model\RecurringPayment\ResponseGetAgreement[]
      */
-    public function getAgreements();
+    public function getAgreements(): array;
 
     /**
      * @return \zaporylie\Vipps\Model\RecurringPayment\ResponseGetAgreement
      */
-    public function getAgreement($agreement_id);
+    public function getAgreement(string $agreement_id): ResponseGetAgreement;
 
     /**
      * @param $agreement_id
@@ -38,14 +43,14 @@ public function getAgreement($agreement_id);
      *
      * @return \zaporylie\Vipps\Model\RecurringPayment\ResponseUpdateAgreement
      */
-    public function updateAgreement($agreement_id, RequestUpdateAgreement $request);
+    public function updateAgreement(string $agreement_id, RequestUpdateAgreement $request): ResponseUpdateAgreement;
 
     /**
      * @param $agreement_id
      *
      * @return \zaporylie\Vipps\Model\RecurringPayment\Charge[]
      */
-    public function getCharges($agreement_id);
+    public function getCharges(string $agreement_id): array;
 
     /**
      * @param $agreement_id
@@ -53,7 +58,7 @@ public function getCharges($agreement_id);
      *
      * @return \zaporylie\Vipps\Model\RecurringPayment\Charge
      */
-    public function getCharge($agreement_id, $charge_id);
+    public function getCharge(string $agreement_id, string $charge_id): Charge;
 
     /**
      * @param $agreement_id
@@ -61,7 +66,7 @@ public function getCharge($agreement_id, $charge_id);
      *
      * @return \zaporylie\Vipps\Model\RecurringPayment\ResponseCreateCharge
      */
-    public function createCharge($agreement_id, RequestCreateCharge $request);
+    public function createCharge(string $agreement_id, RequestCreateCharge $request): ResponseCreateCharge;
 
     /**
      * @param string $agreement_id
@@ -69,7 +74,7 @@ public function createCharge($agreement_id, RequestCreateCharge $request);
      *
      * @return string
      */
-    public function cancelCharge($agreement_id, $charge_id);
+    public function cancelCharge(string $agreement_id, string $charge_id): string;
 
     /**
      * @param string $agreement_id
@@ -77,7 +82,7 @@ public function cancelCharge($agreement_id, $charge_id);
      *
      * @return string
      */
-    public function captureCharge($agreement_id, $charge_id);
+    public function captureCharge(string $agreement_id, string $charge_id): string;
 
     /**
      * @param string $agreement_id
@@ -86,5 +91,5 @@ public function captureCharge($agreement_id, $charge_id);
      *
      * @return string
      */
-    public function refundCharge($agreement_id, $charge_id, RequestRefundCharge $requestObject);
+    public function refundCharge(string $agreement_id, string $charge_id, RequestRefundCharge $requestObject): string;
 }
diff --git a/src/Api/UserInfo.php b/src/Api/UserInfo.php
index 155a43d..82aae3f 100644
--- a/src/Api/UserInfo.php
+++ b/src/Api/UserInfo.php
@@ -2,6 +2,7 @@
 
 namespace zaporylie\Vipps\Api;
 
+use zaporylie\Vipps\Model\UserInfo\ResponseUserInfo;
 use zaporylie\Vipps\Resource\UserInfo\UserInfo as UserInfoResource;
 use zaporylie\Vipps\VippsInterface;
 
@@ -26,7 +27,7 @@ public function __construct(VippsInterface $app)
     /**
      * {@inheritdoc}
      */
-    public function userInfo($sub)
+    public function userInfo(string $sub): ResponseUserInfo
     {
         $resource = new UserInfoResource($this->app, $sub);
         /** @var \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo $response */
diff --git a/src/Api/UserInfoInterface.php b/src/Api/UserInfoInterface.php
index dfa48f9..d1340b0 100644
--- a/src/Api/UserInfoInterface.php
+++ b/src/Api/UserInfoInterface.php
@@ -2,6 +2,8 @@
 
 namespace zaporylie\Vipps\Api;
 
+use zaporylie\Vipps\Model\UserInfo\ResponseUserInfo;
+
 /**
  * Interface UserInfoInterface
  *
@@ -15,5 +17,5 @@ interface UserInfoInterface
      *
      * @return \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo
      */
-    public function userInfo($sub);
+    public function userInfo(string $sub): ResponseUserInfo;
 }
diff --git a/src/Authentication/TokenMemoryCacheStorage.php b/src/Authentication/TokenMemoryCacheStorage.php
index 52584ed..37910c7 100644
--- a/src/Authentication/TokenMemoryCacheStorage.php
+++ b/src/Authentication/TokenMemoryCacheStorage.php
@@ -21,7 +21,7 @@ class TokenMemoryCacheStorage implements TokenStorageInterface
     /**
      * {@inheritdoc}
      */
-    public function get()
+    public function get(): ResponseGetToken
     {
         if (!$this->has()) {
             throw new InvalidArgumentException('Missing Token');
@@ -32,7 +32,7 @@ public function get()
     /**
      * {@inheritdoc}
      */
-    public function set(ResponseGetToken $token)
+    public function set(ResponseGetToken $token): TokenStorageInterface
     {
         $this->token = $token;
         return $this;
@@ -41,7 +41,7 @@ public function set(ResponseGetToken $token)
     /**
      * {@inheritdoc}
      */
-    public function has()
+    public function has(): bool
     {
         if (!($this->token instanceof ResponseGetToken)) {
             return false;
@@ -58,7 +58,7 @@ public function has()
     /**
      * {@inheritdoc}
      */
-    public function delete()
+    public function delete(): TokenStorageInterface
     {
         $this->token = null;
         return $this;
@@ -67,7 +67,7 @@ public function delete()
     /**
      * {@inheritdoc}
      */
-    public function clear()
+    public function clear(): TokenStorageInterface
     {
         $this->delete();
         return $this;
diff --git a/src/Authentication/TokenStorageInterface.php b/src/Authentication/TokenStorageInterface.php
index 3717d2d..89f1c67 100644
--- a/src/Authentication/TokenStorageInterface.php
+++ b/src/Authentication/TokenStorageInterface.php
@@ -16,27 +16,27 @@ interface TokenStorageInterface
      * @return \zaporylie\Vipps\Model\Authorization\ResponseGetToken
      * @throws \zaporylie\Vipps\Exceptions\Authentication\InvalidArgumentException
      */
-    public function get();
+    public function get() : ResponseGetToken;
 
     /**
      * @param \zaporylie\Vipps\Model\Authorization\ResponseGetToken $token
      *
      * @return self
      */
-    public function set(ResponseGetToken $token);
+    public function set(ResponseGetToken $token): self;
 
     /**
      * @return bool
      */
-    public function has();
+    public function has(): bool;
 
     /**
      * @return self
      */
-    public function delete();
+    public function delete(): self;
 
     /**
      * @return self
      */
-    public function clear();
+    public function clear(): self;
 }
diff --git a/src/Client.php b/src/Client.php
index 4db8f09..e091343 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -20,37 +20,37 @@ class Client implements ClientInterface
     /**
      * @var \Psr\Http\Client\ClientInterface
      */
-    protected $httpClient;
+    protected HttpClientInterface $httpClient;
 
     /**
      * @var \zaporylie\Vipps\EndpointInterface
      */
-    protected $endpoint;
+    protected EndpointInterface $endpoint;
 
     /**
      * @var \Psr\Http\Message\RequestFactoryInterface
      */
-    protected $requestFactory;
+    protected RequestFactoryInterface $requestFactory;
 
     /**
      * @var string
      */
-    protected $token;
+    protected string $token;
 
     /**
      * @var string
      */
-    protected $tokenType;
+    protected string $tokenType;
 
     /**
      * @var \zaporylie\Vipps\Authentication\TokenStorageInterface
      */
-    protected $tokenStorage;
+    protected TokenStorageInterface $tokenStorage;
 
     /**
      * @var string
      */
-    protected $clientId;
+    protected string $clientId;
 
     /**
      * VippsClient constructor.
@@ -90,7 +90,7 @@ public function __construct($client_id, array $options = [])
      *
      * @return string
      */
-    public function getToken()
+    public function getToken(): string
     {
         if (!isset($this->token)) {
             throw new InvalidArgumentException('Missing Token');
@@ -99,34 +99,26 @@ public function getToken()
     }
 
     /**
-     * Gets tokenStorage value.
-     *
-     * @return \zaporylie\Vipps\Authentication\TokenStorageInterface
+     * {inheritdoc}
      */
-    public function getTokenStorage()
+    public function getTokenStorage(): TokenStorageInterface
     {
         return $this->tokenStorage;
     }
 
     /**
-     * Sets tokenStorage variable.
-     *
-     * @param \zaporylie\Vipps\Authentication\TokenStorageInterface $tokenStorage
-     *
-     * @return $this
+     * {inheritdoc}
      */
-    public function setTokenStorage(TokenStorageInterface $tokenStorage)
+    public function setTokenStorage(TokenStorageInterface $tokenStorage): self
     {
         $this->tokenStorage = $tokenStorage;
         return $this;
     }
 
     /**
-     * Gets clientId value.
-     *
-     * @return string
+     * {inheritdoc}
      */
-    public function getClientId()
+    public function getClientId(): string
     {
         if (!isset($this->clientId)) {
             throw new InvalidArgumentException('Missing Client ID');
@@ -135,13 +127,9 @@ public function getClientId()
     }
 
     /**
-     * Sets clientId variable.
-     *
-     * @param string $clientId
-     *
-     * @return $this
+     * {inheritdoc}
      */
-    public function setClientId($clientId)
+    public function setClientId(string $clientId): self
     {
         $this->clientId = $clientId;
         return $this;
@@ -158,7 +146,7 @@ public function getEndpoint(): EndpointInterface
     /**
      * {@inheritdoc}
      */
-    public function setEndpoint(EndpointInterface $endpoint)
+    public function setEndpoint(EndpointInterface $endpoint): self
     {
         $this->endpoint = $endpoint;
         return $this;
@@ -175,7 +163,7 @@ public function getHttpClient(): HttpClientInterface
     /**
      * {@inheritdoc}
      */
-    public function setHttpClient(?HttpClientInterface $httpClient)
+    public function setHttpClient(?HttpClientInterface $httpClient): self
     {
         $this->httpClient = self::httpClientDiscovery($httpClient);
         unset($this->requestFactory);
diff --git a/src/ClientInterface.php b/src/ClientInterface.php
index 14a68af..8aee3a8 100644
--- a/src/ClientInterface.php
+++ b/src/ClientInterface.php
@@ -11,21 +11,21 @@ interface ClientInterface
     /**
      * @return \zaporylie\Vipps\Authentication\TokenStorageInterface
      */
-    public function getTokenStorage();
+    public function getTokenStorage(): TokenStorageInterface;
 
     /**
      * @param \zaporylie\Vipps\Authentication\TokenStorageInterface $tokenStorage
      *
      * @return $this
      */
-    public function setTokenStorage(TokenStorageInterface $tokenStorage);
+    public function setTokenStorage(TokenStorageInterface $tokenStorage): self;
 
     /**
      * Gets clientId value.
      *
      * @return string
      */
-    public function getClientId();
+    public function getClientId(): string;
 
     /**
      * Sets clientId variable.
@@ -34,7 +34,7 @@ public function getClientId();
      *
      * @return $this
      */
-    public function setClientId($clientId);
+    public function setClientId(string $clientId): self;
 
     /**
      * Gets connection value.
@@ -50,7 +50,7 @@ public function getEndpoint(): EndpointInterface;
      *
      * @return $this
      */
-    public function setEndpoint(EndpointInterface $endpoint);
+    public function setEndpoint(EndpointInterface $endpoint): self;
 
     /**
      * Gets httpClient value.
diff --git a/src/Endpoint.php b/src/Endpoint.php
index 4b57e79..5de07a9 100644
--- a/src/Endpoint.php
+++ b/src/Endpoint.php
@@ -10,7 +10,7 @@
 
 use Eloquent\Enumeration\AbstractMultiton;
 use Http\Discovery\Psr17FactoryDiscovery;
-use Http\Discovery\UriFactoryDiscovery;
+use Psr\Http\Message\UriInterface;
 
 /**
  * Class ConnectionBase
@@ -34,10 +34,10 @@ class Endpoint extends AbstractMultiton implements EndpointInterface
         'path' => '',
     ];
 
-    protected $scheme;
-    protected $host;
-    protected $port;
-    protected $path;
+    protected string $scheme;
+    protected string $host;
+    protected string $port;
+    protected string $path;
 
     /**
      * {@inheritdoc}
@@ -66,51 +66,41 @@ protected function __construct($key, $scheme, $host, $port, $path)
     }
 
     /**
-     * Gets scheme value.
-     *
-     * @return string
+     * {@inheritdoc}
      */
-    public function getScheme()
+    public function getScheme(): string
     {
         return $this->scheme;
     }
 
     /**
-     * Gets host value.
-     *
-     * @return string
+     * {@inheritdoc}
      */
-    public function getHost()
+    public function getHost(): string
     {
         return $this->host;
     }
 
     /**
-     * Gets port value.
-     *
-     * @return string
+     * {@inheritdoc}
      */
-    public function getPort()
+    public function getPort(): string
     {
         return $this->port;
     }
 
     /**
-     * Gets path value.
-     *
-     * @return string
+     * {@inheritdoc}
      */
-    public function getPath()
+    public function getPath(): string
     {
         return $this->path;
     }
 
     /**
-     * Get connection base uri.
-     *
-     * @return \Psr\Http\Message\UriInterface
+     * {@inheritdoc}
      */
-    public function getUri()
+    public function getUri(): UriInterface
     {
         $uri = Psr17FactoryDiscovery::findUriFactory();
         return $uri->createUri(sprintf(
diff --git a/src/EndpointInterface.php b/src/EndpointInterface.php
index 9a424a2..ca454e2 100644
--- a/src/EndpointInterface.php
+++ b/src/EndpointInterface.php
@@ -8,8 +8,11 @@
 
 namespace zaporylie\Vipps;
 
+use Psr\Http\Message\UriInterface;
+
 /**
  * Interface ConnectionInterface
+ *
  * @package Vipps
  * @subpackage Connection
  */
@@ -19,27 +22,27 @@ interface EndpointInterface
     /**
      * @return string
      */
-    public function getScheme();
+    public function getScheme(): string;
 
     /**
      * @return string
      */
-    public function getHost();
+    public function getHost(): string;
 
     /**
      * @return string
      */
-    public function getPort();
+    public function getPort(): string;
 
     /**
      * @return string
      */
-    public function getPath();
+    public function getPath(): string;
 
     /**
      * Returns base URI for requests against VIPPS servers.
      *
      * @return \Psr\Http\Message\UriInterface
      */
-    public function getUri();
+    public function getUri(): UriInterface;
 }
diff --git a/src/Exceptions/VippsException.php b/src/Exceptions/VippsException.php
index 6dff525..16979f0 100644
--- a/src/Exceptions/VippsException.php
+++ b/src/Exceptions/VippsException.php
@@ -24,7 +24,7 @@ class VippsException extends \Exception
     /**
      * @var \zaporylie\Vipps\Model\Error\ErrorInterface|null
      */
-    protected $error;
+    protected ?ErrorInterface $error;
 
     /**
      * VippsException constructor.
@@ -34,7 +34,7 @@ class VippsException extends \Exception
      * @param \Exception|null $previous
      * @param \zaporylie\Vipps\Model\Error\ErrorInterface|null $error
      */
-    public function __construct($message = '', $code = 0, \Exception $previous = null, ErrorInterface $error = null)
+    public function __construct($message = '', $code = 0, \Exception $previous = null, ?ErrorInterface $error = null)
     {
         parent::__construct($message, $code, $previous);
         $this->error = $error;
@@ -99,7 +99,7 @@ public static function createFromResponse(
         ResponseInterface $response,
         $serializer = null,
         $force = true
-    ) {
+    ): ?VippsException {
 
         // If error code tells us that something went wrong we must accept it.
         if (!$force && $response->getStatusCode() >= 400) {
diff --git a/src/Model/UserInfo/AccountInfo.php b/src/Model/UserInfo/AccountInfo.php
index 7744d4e..a1ba036 100644
--- a/src/Model/UserInfo/AccountInfo.php
+++ b/src/Model/UserInfo/AccountInfo.php
@@ -9,23 +9,53 @@
  *
  * @package Vipps\Model\UserInfo
  */
-class AccountInfo
+final class AccountInfo
 {
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $account_name;
+    protected string $account_name;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $account_number;
+    protected string $account_number;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $bank_name;
+    protected string $bank_name;
+
+    /**
+     * Gets account_name value.
+     *
+     * @return string
+     */
+    public function getAccountName(): string
+    {
+        return $this->account_name;
+    }
+
+    /**
+     * Gets account_number value.
+     *
+     * @return string
+     */
+    public function getAccountNumber(): string
+    {
+        return $this->account_number;
+    }
+
+    /**
+     * Gets bank_name value.
+     *
+     * @return string
+     */
+    public function getBankName(): string
+    {
+        return $this->bank_name;
+    }
 }
diff --git a/src/Model/UserInfo/Address.php b/src/Model/UserInfo/Address.php
index b4a4b35..ef07baf 100644
--- a/src/Model/UserInfo/Address.php
+++ b/src/Model/UserInfo/Address.php
@@ -9,50 +9,50 @@
  *
  * @package Vipps\Model\UserInfo
  */
-class Address
+final class Address
 {
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $address_type;
+    protected string $address_type;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $street_address;
+    protected string $street_address;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $region;
+    protected string $region;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $country;
+    protected string $country;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $postal_code;
+    protected string $postal_code;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $formatted;
+    protected string $formatted;
 
     /**
      * Gets address_type value.
      *
      * @return string
      */
-    public function getAddressType()
+    public function getAddressType(): string
     {
         return $this->address_type;
     }
@@ -62,7 +62,7 @@ public function getAddressType()
      *
      * @return string
      */
-    public function getStreetAddress()
+    public function getStreetAddress(): string
     {
         return $this->street_address;
     }
@@ -72,7 +72,7 @@ public function getStreetAddress()
      *
      * @return string
      */
-    public function getRegion()
+    public function getRegion(): string
     {
         return $this->region;
     }
@@ -82,7 +82,7 @@ public function getRegion()
      *
      * @return string
      */
-    public function getCountry()
+    public function getCountry(): string
     {
         return $this->country;
     }
@@ -92,7 +92,7 @@ public function getCountry()
      *
      * @return string
      */
-    public function getPostalCode()
+    public function getPostalCode(): string
     {
         return $this->postal_code;
     }
@@ -102,7 +102,7 @@ public function getPostalCode()
      *
      * @return string
      */
-    public function getFormatted()
+    public function getFormatted(): string
     {
         return $this->formatted;
     }
diff --git a/src/Model/UserInfo/ResponseUserInfo.php b/src/Model/UserInfo/ResponseUserInfo.php
index 77115ad..71de5b0 100644
--- a/src/Model/UserInfo/ResponseUserInfo.php
+++ b/src/Model/UserInfo/ResponseUserInfo.php
@@ -4,92 +4,92 @@
 
 use JMS\Serializer\Annotation as Serializer;
 
-class ResponseUserInfo
+final class ResponseUserInfo
 {
     /**
      * @var \zaporylie\Vipps\Model\UserInfo\AccountInfo[]
      * @Serializer\Type("array<zaporylie\Vipps\Model\UserInfo\AccountInfo>")
      */
-    protected $accounts;
+    protected array $accounts;
 
     /**
      * @var \zaporylie\Vipps\Model\UserInfo\Address
      * @Serializer\Type("zaporylie\Vipps\Model\UserInfo\Address")
      */
-    protected $address;
+    protected Address $address;
 
     /**
      * @var \zaporylie\Vipps\Model\UserInfo\Address[]
      * @Serializer\Type("array<zaporylie\Vipps\Model\UserInfo\Address>")
      */
-    protected $other_addresses;
+    protected array $other_addresses;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $birthday;
+    protected string $birthdate;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $email;
+    protected string $email;
 
     /**
      * @var bool
      * @Serializer\Type("boolean")
      */
-    protected $email_verified;
+    protected bool $email_verified;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $family_name;
+    protected string $family_name;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $given_name;
+    protected string $given_name;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $name;
+    protected string $name;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $nin;
+    protected string $nin;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $phone_number;
+    protected string $phone_number;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $sid;
+    protected string $sid;
 
     /**
      * @var string
      * @Serializer\Type("string")
      */
-    protected $sub;
+    protected string $sub;
 
     /**
      * Gets accounts value.
      *
      * @return \zaporylie\Vipps\Model\UserInfo\AccountInfo[]
      */
-    public function getAccounts()
+    public function getAccounts(): array
     {
         return $this->accounts;
     }
@@ -99,19 +99,19 @@ public function getAccounts()
      *
      * @return \zaporylie\Vipps\Model\UserInfo\Address
      */
-    public function getAddress()
+    public function getAddress(): Address
     {
         return $this->address;
     }
 
     /**
-     * Gets birthday value.
+     * Gets birthdate value.
      *
      * @return string
      */
-    public function getBirthday()
+    public function getBirthdate(): string
     {
-        return $this->birthday;
+        return $this->birthdate;
     }
 
     /**
@@ -119,7 +119,7 @@ public function getBirthday()
      *
      * @return string
      */
-    public function getEmail()
+    public function getEmail(): string
     {
         return $this->email;
     }
@@ -129,7 +129,7 @@ public function getEmail()
      *
      * @return string
      */
-    public function getFamilyName()
+    public function getFamilyName(): string
     {
         return $this->family_name;
     }
@@ -139,7 +139,7 @@ public function getFamilyName()
      *
      * @return string
      */
-    public function getGivenName()
+    public function getGivenName(): string
     {
         return $this->given_name;
     }
@@ -149,7 +149,7 @@ public function getGivenName()
      *
      * @return string
      */
-    public function getName()
+    public function getName(): string
     {
         return $this->name;
     }
@@ -159,7 +159,7 @@ public function getName()
      *
      * @return string
      */
-    public function getNin()
+    public function getNin(): string
     {
         return $this->nin;
     }
@@ -169,7 +169,7 @@ public function getNin()
      *
      * @return \zaporylie\Vipps\Model\UserInfo\Address[]
      */
-    public function getOtherAddresses()
+    public function getOtherAddresses(): array
     {
         return $this->other_addresses;
     }
@@ -179,7 +179,7 @@ public function getOtherAddresses()
      *
      * @return string
      */
-    public function getPhoneNumber()
+    public function getPhoneNumber(): string
     {
         return $this->phone_number;
     }
@@ -189,7 +189,7 @@ public function getPhoneNumber()
      *
      * @return string
      */
-    public function getSid()
+    public function getSid(): string
     {
         return $this->sid;
     }
@@ -199,7 +199,7 @@ public function getSid()
      *
      * @return string
      */
-    public function getSub()
+    public function getSub(): string
     {
         return $this->sub;
     }
diff --git a/src/Resource/Authorization/GetToken.php b/src/Resource/Authorization/GetToken.php
index ac12b83..7aa92fa 100644
--- a/src/Resource/Authorization/GetToken.php
+++ b/src/Resource/Authorization/GetToken.php
@@ -15,15 +15,10 @@
 class GetToken extends ResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod;
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/accessToken/get';
+    protected string $path = '/accessToken/get';
 
     /**
      * GetToken constructor.
@@ -34,6 +29,7 @@ class GetToken extends ResourceBase
      */
     public function __construct(VippsInterface $vipps, $subscription_key, $client_secret)
     {
+        $this->method = HttpMethod::POST();
         parent::__construct($vipps, $subscription_key);
         // Authorization module requires client_id to be set on "client_id"
         // header.
diff --git a/src/Resource/IdempotencyKeyFactory.php b/src/Resource/IdempotencyKeyFactory.php
index c18e6b6..cadfeff 100644
--- a/src/Resource/IdempotencyKeyFactory.php
+++ b/src/Resource/IdempotencyKeyFactory.php
@@ -15,7 +15,7 @@ abstract class IdempotencyKeyFactory
      *
      * @return string
      */
-    public static function generate()
+    public static function generate(): string
     {
         return uniqid('', true);
     }
diff --git a/src/Resource/Payment/CancelPayment.php b/src/Resource/Payment/CancelPayment.php
index 02b59c8..bade558 100644
--- a/src/Resource/Payment/CancelPayment.php
+++ b/src/Resource/Payment/CancelPayment.php
@@ -15,15 +15,10 @@
 class CancelPayment extends PaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::PUT;
-
     /**
      * @var string
      */
-    protected $path = '/ecomm/v2/payments/{id}/cancel';
+    protected string $path = '/ecomm/v2/payments/{id}/cancel';
 
     /**
      * InitiatePayment constructor.
@@ -40,6 +35,7 @@ public function __construct(
         RequestCancelPayment $requestObject
     ) {
         parent::__construct($vipps, $subscription_key);
+        $this->method = HttpMethod::PUT();
         $this->body = $this
             ->getSerializer()
             ->serialize(
diff --git a/src/Resource/Payment/CapturePayment.php b/src/Resource/Payment/CapturePayment.php
index 0204d4a..7d3c292 100644
--- a/src/Resource/Payment/CapturePayment.php
+++ b/src/Resource/Payment/CapturePayment.php
@@ -15,15 +15,10 @@
 class CapturePayment extends PaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/ecomm/v2/payments/{id}/capture';
+    protected string $path = '/ecomm/v2/payments/{id}/capture';
 
     /**
      * InitiatePayment constructor.
@@ -39,6 +34,7 @@ public function __construct(
         $order_id,
         RequestCapturePayment $requestObject
     ) {
+        $this->method = HttpMethod::POST();
         parent::__construct($vipps, $subscription_key);
         $this->body = $this
             ->getSerializer()
diff --git a/src/Resource/Payment/GetOrderStatus.php b/src/Resource/Payment/GetOrderStatus.php
index e78a6d3..d297536 100644
--- a/src/Resource/Payment/GetOrderStatus.php
+++ b/src/Resource/Payment/GetOrderStatus.php
@@ -17,15 +17,10 @@
 class GetOrderStatus extends PaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::GET;
-
     /**
      * @var string
      */
-    protected $path = '/ecomm/v2/payments/{id}/status';
+    protected string $path = '/ecomm/v2/payments/{id}/status';
 
     /**
      * InitiatePayment constructor.
@@ -36,6 +31,7 @@ class GetOrderStatus extends PaymentResourceBase
      */
     public function __construct(VippsInterface $vipps, $subscription_key, $order_id)
     {
+        $this->method = HttpMethod::GET();
         parent::__construct($vipps, $subscription_key);
         $this->id = $order_id;
     }
diff --git a/src/Resource/Payment/GetPaymentDetails.php b/src/Resource/Payment/GetPaymentDetails.php
index a234c43..bc5b050 100644
--- a/src/Resource/Payment/GetPaymentDetails.php
+++ b/src/Resource/Payment/GetPaymentDetails.php
@@ -9,15 +9,10 @@
 class GetPaymentDetails extends PaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::GET;
-
     /**
      * @var string
      */
-    protected $path = '/ecomm/v2/payments/{id}/details';
+    protected string $path = '/ecomm/v2/payments/{id}/details';
 
     /**
      * InitiatePayment constructor.
@@ -28,6 +23,7 @@ class GetPaymentDetails extends PaymentResourceBase
      */
     public function __construct(VippsInterface $vipps, $subscription_key, $order_id)
     {
+        $this->method = HttpMethod::GET();
         parent::__construct($vipps, $subscription_key);
         $this->id = $order_id;
     }
diff --git a/src/Resource/Payment/InitiatePayment.php b/src/Resource/Payment/InitiatePayment.php
index 9b8af3a..f4fc58d 100644
--- a/src/Resource/Payment/InitiatePayment.php
+++ b/src/Resource/Payment/InitiatePayment.php
@@ -15,15 +15,10 @@
 class InitiatePayment extends PaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/ecomm/v2/payments';
+    protected string $path = '/ecomm/v2/payments';
 
     /**
      * InitiatePayment constructor.
@@ -34,6 +29,7 @@ class InitiatePayment extends PaymentResourceBase
      */
     public function __construct(VippsInterface $vipps, $subscription_key, RequestInitiatePayment $requestObject)
     {
+        $this->method = HttpMethod::POST();
         parent::__construct($vipps, $subscription_key);
         $this->body = $this
             ->getSerializer()
diff --git a/src/Resource/Payment/RefundPayment.php b/src/Resource/Payment/RefundPayment.php
index 91c84a1..64457cb 100644
--- a/src/Resource/Payment/RefundPayment.php
+++ b/src/Resource/Payment/RefundPayment.php
@@ -15,15 +15,10 @@
 class RefundPayment extends PaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/ecomm/v2/payments/{id}/refund';
+    protected string $path = '/ecomm/v2/payments/{id}/refund';
 
     /**
      * InitiatePayment constructor.
@@ -39,6 +34,7 @@ public function __construct(
         $order_id,
         RequestRefundPayment $requestObject
     ) {
+        $this->method = HttpMethod::POST();
         parent::__construct($vipps, $subscription_key);
         $this->body = $this
             ->getSerializer()
diff --git a/src/Resource/PaymentsInterface.php b/src/Resource/PaymentsInterface.php
index 0ee19d7..adc7460 100644
--- a/src/Resource/PaymentsInterface.php
+++ b/src/Resource/PaymentsInterface.php
@@ -21,7 +21,7 @@ interface PaymentsInterface extends ResourceInterface
      * @param string $orderID
      * @return $this
      */
-    public function setOrderID($orderID);
+    public function setOrderID(string $orderID): self;
 
     /**
      * Create new payment.
@@ -36,11 +36,11 @@ public function setOrderID($orderID);
      *   Callback absolute Url.
      * @param string $fallback
      *   Fallback absolute Url.
-     * @param null $refOrderID
+     * @param string|null $refOrderID
      *   (optional) Reference to previous order.
      * @return $this
      */
-    public function create($mobileNumber, $amount, $text, $callback, $fallback, $refOrderID = null);
+    public function create(int $mobileNumber, int $amount, string $text, string $callback, string $fallback, string $refOrderID = null): self;
 
     /**
      * Cancel payment.
@@ -48,7 +48,7 @@ public function create($mobileNumber, $amount, $text, $callback, $fallback, $ref
      * @param string $text
      * @return $this
      */
-    public function cancel($text);
+    public function cancel(string $text): self;
 
     /**
      * Capture payment.
@@ -59,7 +59,7 @@ public function cancel($text);
      *   (optional) Amount in øre.
      * @return $this
      */
-    public function capture($text, $amount = 0);
+    public function capture(string $text, int $amount = 0): self;
 
     /**
      * Refund payment.
@@ -70,7 +70,7 @@ public function capture($text, $amount = 0);
      *   (optional) Amount in øre.
      * @return $this
      */
-    public function refund($text, $amount = 0);
+    public function refund(string $text, int $amount = 0): self;
 
     /**
      * Get payment status.
diff --git a/src/Resource/RecurringPayment/CancelCharge.php b/src/Resource/RecurringPayment/CancelCharge.php
index c734f2c..034210a 100644
--- a/src/Resource/RecurringPayment/CancelCharge.php
+++ b/src/Resource/RecurringPayment/CancelCharge.php
@@ -18,15 +18,10 @@
 class CancelCharge extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::DELETE;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}/charges/{charge_id}';
+    protected string $path = '/recurring/v2/agreements/{id}/charges/{charge_id}';
 
     /**
      * CancelCharge constructor.
@@ -45,6 +40,7 @@ public function __construct(
         $this->id = $agreement_id;
         $this->charge_id = $charge_id;
         parent::__construct($vipps, $subscription_key);
+        $this->method = HttpMethod::DELETE();
     }
 
     /**
diff --git a/src/Resource/RecurringPayment/CaptureCharge.php b/src/Resource/RecurringPayment/CaptureCharge.php
index cdc536b..61c2c67 100644
--- a/src/Resource/RecurringPayment/CaptureCharge.php
+++ b/src/Resource/RecurringPayment/CaptureCharge.php
@@ -18,15 +18,10 @@
 class CaptureCharge extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}/charges/{charge_id}/capture';
+    protected string $path = '/recurring/v2/agreements/{id}/charges/{charge_id}/capture';
 
     /**
      * InitiatePayment constructor.
@@ -47,6 +42,7 @@ public function __construct(
         // By default RequestID is different for each Resource object.
         $this->headers['Idempotency-Key'] = IdempotencyKeyFactory::generate();
         parent::__construct($vipps, $subscription_key);
+        $this->method = HttpMethod::POST();
     }
 
     /**
diff --git a/src/Resource/RecurringPayment/CreateAgreement.php b/src/Resource/RecurringPayment/CreateAgreement.php
index ed05aee..8ca5d3b 100644
--- a/src/Resource/RecurringPayment/CreateAgreement.php
+++ b/src/Resource/RecurringPayment/CreateAgreement.php
@@ -15,15 +15,10 @@
 class CreateAgreement extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements';
+    protected string $path = '/recurring/v2/agreements';
 
     /**
      * InitiatePayment constructor.
@@ -35,6 +30,7 @@ class CreateAgreement extends RecurringPaymentResourceBase
     public function __construct(VippsInterface $vipps, $subscription_key, RequestCreateAgreement $requestObject)
     {
         parent::__construct($vipps, $subscription_key);
+        $this->method = HttpMethod::POST();
         $this->body = $this
             ->getSerializer()
             ->serialize(
diff --git a/src/Resource/RecurringPayment/CreateCharge.php b/src/Resource/RecurringPayment/CreateCharge.php
index e86bcec..7da4548 100644
--- a/src/Resource/RecurringPayment/CreateCharge.php
+++ b/src/Resource/RecurringPayment/CreateCharge.php
@@ -17,15 +17,10 @@
 class CreateCharge extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}/charges';
+    protected string $path = '/recurring/v2/agreements/{id}/charges';
 
     /**
      * InitiatePayment constructor.
@@ -45,6 +40,7 @@ public function __construct(
         // By default RequestID is different for each Resource object.
         $this->headers['Idempotency-Key'] = IdempotencyKeyFactory::generate();
         parent::__construct($vipps, $subscription_key);
+        $this->method = HttpMethod::POST();
         $this->body = $this
             ->getSerializer()
             ->serialize(
diff --git a/src/Resource/RecurringPayment/GetAgreement.php b/src/Resource/RecurringPayment/GetAgreement.php
index 8333028..e836de7 100644
--- a/src/Resource/RecurringPayment/GetAgreement.php
+++ b/src/Resource/RecurringPayment/GetAgreement.php
@@ -14,15 +14,10 @@
 class GetAgreement extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::GET;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}';
+    protected string $path = '/recurring/v2/agreements/{id}';
 
     /**
      * InitiatePayment constructor.
diff --git a/src/Resource/RecurringPayment/GetAgreements.php b/src/Resource/RecurringPayment/GetAgreements.php
index 0d6a559..65fb2ce 100644
--- a/src/Resource/RecurringPayment/GetAgreements.php
+++ b/src/Resource/RecurringPayment/GetAgreements.php
@@ -4,6 +4,7 @@
 
 use zaporylie\Vipps\Model\RecurringPayment\ResponseGetAgreement;
 use zaporylie\Vipps\Resource\HttpMethod;
+use zaporylie\Vipps\VippsInterface;
 
 /**
  * Class GetAgreements
@@ -13,15 +14,10 @@
 class GetAgreements extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::GET;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements';
+    protected string $path = '/recurring/v2/agreements';
 
     /**
      * @return \zaporylie\Vipps\Model\RecurringPayment\ResponseGetAgreement[]
diff --git a/src/Resource/RecurringPayment/GetCharge.php b/src/Resource/RecurringPayment/GetCharge.php
index 3029f10..2ea7f5e 100644
--- a/src/Resource/RecurringPayment/GetCharge.php
+++ b/src/Resource/RecurringPayment/GetCharge.php
@@ -13,15 +13,10 @@
 class GetCharge extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::GET;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}/charges/{charge_id}';
+    protected string $path = '/recurring/v2/agreements/{id}/charges/{charge_id}';
 
     public function __construct(
         \zaporylie\Vipps\VippsInterface $vipps,
diff --git a/src/Resource/RecurringPayment/GetCharges.php b/src/Resource/RecurringPayment/GetCharges.php
index 541b99e..abc72f1 100644
--- a/src/Resource/RecurringPayment/GetCharges.php
+++ b/src/Resource/RecurringPayment/GetCharges.php
@@ -12,16 +12,10 @@
  */
 class GetCharges extends RecurringPaymentResourceBase
 {
-
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::GET;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}/charges';
+    protected string $path = '/recurring/v2/agreements/{id}/charges';
 
     public function __construct(
         \zaporylie\Vipps\VippsInterface $vipps,
diff --git a/src/Resource/RecurringPayment/RecurringPaymentResourceBase.php b/src/Resource/RecurringPayment/RecurringPaymentResourceBase.php
index 7af5980..e75f912 100644
--- a/src/Resource/RecurringPayment/RecurringPaymentResourceBase.php
+++ b/src/Resource/RecurringPayment/RecurringPaymentResourceBase.php
@@ -6,6 +6,7 @@
 use JMS\Serializer\Naming\SerializedNameAnnotationStrategy;
 use JMS\Serializer\SerializerBuilder;
 use zaporylie\Vipps\Resource\AuthorizedResourceBase;
+use zaporylie\Vipps\Resource\HttpMethod;
 use zaporylie\Vipps\Resource\RequestIdFactory;
 
 /**
@@ -26,6 +27,7 @@ abstract class RecurringPaymentResourceBase extends AuthorizedResourceBase
      */
     public function __construct(\zaporylie\Vipps\VippsInterface $vipps, $subscription_key)
     {
+        $this->method = HttpMethod::GET();
         parent::__construct($vipps, $subscription_key);
 
         // Adjust serializer.
@@ -49,7 +51,7 @@ public function __construct(\zaporylie\Vipps\VippsInterface $vipps, $subscriptio
      *
      * All occurrences of {id} pattern will be replaced with $this->id
      */
-    public function getPath()
+    public function getPath(): string
     {
         $path = parent::getPath();
         // If ID is set replace {id} pattern with model's ID.
diff --git a/src/Resource/RecurringPayment/RefundCharge.php b/src/Resource/RecurringPayment/RefundCharge.php
index 6bdcb3b..13d9591 100644
--- a/src/Resource/RecurringPayment/RefundCharge.php
+++ b/src/Resource/RecurringPayment/RefundCharge.php
@@ -19,15 +19,10 @@
 class RefundCharge extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::POST;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}/charges/{charge_id}/refund';
+    protected string $path = '/recurring/v2/agreements/{id}/charges/{charge_id}/refund';
 
     /**
      * RefundCharge constructor.
@@ -50,6 +45,7 @@ public function __construct(
         // By default RequestID is different for each Resource object.
         $this->headers['Idempotency-Key'] = IdempotencyKeyFactory::generate();
         parent::__construct($vipps, $subscription_key);
+        $this->method = HttpMethod::POST();
         $this->body = $this
             ->getSerializer()
             ->serialize(
diff --git a/src/Resource/RecurringPayment/UpdateAgreement.php b/src/Resource/RecurringPayment/UpdateAgreement.php
index b9c0133..30007c3 100644
--- a/src/Resource/RecurringPayment/UpdateAgreement.php
+++ b/src/Resource/RecurringPayment/UpdateAgreement.php
@@ -15,15 +15,10 @@
 class UpdateAgreement extends RecurringPaymentResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::PATCH;
-
     /**
      * @var string
      */
-    protected $path = '/recurring/v2/agreements/{id}';
+    protected string $path = '/recurring/v2/agreements/{id}';
 
     /**
      * InitiatePayment constructor.
@@ -40,6 +35,7 @@ public function __construct(
         RequestUpdateAgreement $requestObject
     ) {
         parent::__construct($vipps, $subscription_key);
+        $this->method = HttpMethod::PATCH();
         $this->id = $agreement_id;
         $this->body = $this
             ->getSerializer()
diff --git a/src/Resource/RequestIdFactory.php b/src/Resource/RequestIdFactory.php
index 6c38a41..e11b546 100644
--- a/src/Resource/RequestIdFactory.php
+++ b/src/Resource/RequestIdFactory.php
@@ -15,7 +15,7 @@ abstract class RequestIdFactory
      *
      * @return string
      */
-    public static function generate()
+    public static function generate(): string
     {
         return uniqid('', true);
     }
diff --git a/src/Resource/ResourceBase.php b/src/Resource/ResourceBase.php
index b243df9..d1e9ca1 100644
--- a/src/Resource/ResourceBase.php
+++ b/src/Resource/ResourceBase.php
@@ -12,9 +12,11 @@
 use Http\Client\Exception\HttpException;
 use Http\Client\HttpAsyncClient;
 use Http\Client\HttpClient;
+use JMS\Serializer\Serializer;
 use JMS\Serializer\SerializerBuilder;
 use Psr\Http\Client\ClientInterface;
 use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\UriInterface;
 use zaporylie\Vipps\Exceptions\VippsException;
 use zaporylie\Vipps\VippsInterface;
 
@@ -28,37 +30,37 @@ abstract class ResourceBase implements ResourceInterface, SerializableInterface
     /**
      * @var VippsInterface
      */
-    protected $app;
+    protected VippsInterface $app;
 
     /**
      * @var array
      */
-    protected $headers = [];
+    protected array $headers = [];
 
     /**
      * @var string
      */
-    protected $body = '';
+    protected string $body = '';
 
     /**
      * @var string
      */
-    protected $id;
+    protected string $id;
 
     /**
      * @var string
      */
-    protected $path;
+    protected string $path;
 
     /**
      * @var \zaporylie\Vipps\Resource\HttpMethod
      */
-    protected $method;
+    protected HttpMethod $method;
 
     /**
      * @var \JMS\Serializer\Serializer
      */
-    protected $serializer;
+    protected Serializer $serializer;
 
     /**
      * AbstractResource constructor.
@@ -85,7 +87,7 @@ public function __construct(VippsInterface $vipps, $subscription_key)
      *
      * @return \JMS\Serializer\Serializer
      */
-    public function getSerializer()
+    public function getSerializer(): Serializer
     {
         return $this->serializer;
     }
@@ -93,7 +95,7 @@ public function getSerializer()
     /**
      * {@inheritdoc}
      */
-    public function getHeaders()
+    public function getHeaders(): array
     {
         return $this->headers;
     }
@@ -101,7 +103,7 @@ public function getHeaders()
     /**
      * {@inheritdoc}
      */
-    public function getMethod()
+    public function getMethod(): HttpMethod
     {
         if (!isset($this->method)) {
             throw new \LogicException('Missing HTTP method');
@@ -114,7 +116,7 @@ public function getMethod()
      *
      * All occurrences of {id} pattern will be replaced with $this->id
      */
-    public function getPath()
+    public function getPath(): string
     {
         if (!isset($this->path)) {
             throw new \LogicException('Missing resource path');
@@ -135,7 +137,7 @@ public function getPath()
      *
      * @return $this
      */
-    public function setPath($path)
+    public function setPath($path): self
     {
         $this->path = $path;
         return $this;
@@ -144,7 +146,7 @@ public function setPath($path)
     /**
      * @return string
      */
-    public function getBody()
+    public function getBody(): string
     {
         return $this->body;
     }
@@ -154,7 +156,7 @@ public function getBody()
      *
      * @return \Psr\Http\Message\UriInterface
      */
-    public function getUri($path)
+    public function getUri($path): UriInterface
     {
         return $this->app->getClient()->getEndpoint()->getUri()->withPath($path);
     }
diff --git a/src/Resource/ResourceInterface.php b/src/Resource/ResourceInterface.php
index 770477d..cc54666 100644
--- a/src/Resource/ResourceInterface.php
+++ b/src/Resource/ResourceInterface.php
@@ -22,7 +22,7 @@ interface ResourceInterface
      * @return string
      * @throws \LogicException
      */
-    public function getPath();
+    public function getPath(): string;
 
     /**
      * HTTP method.
@@ -30,7 +30,7 @@ public function getPath();
      * @return \zaporylie\Vipps\Resource\HttpMethod
      * @throws \LogicException
      */
-    public function getMethod();
+    public function getMethod(): HttpMethod;
 
     /**
      * HTTP headers.
@@ -38,7 +38,7 @@ public function getMethod();
      * @return array
      * @throws \LogicException
      */
-    public function getHeaders();
+    public function getHeaders(): array;
 
     /**
      * @return mixed
diff --git a/src/Resource/UserInfo/UserInfo.php b/src/Resource/UserInfo/UserInfo.php
index e9fe519..34b69d9 100644
--- a/src/Resource/UserInfo/UserInfo.php
+++ b/src/Resource/UserInfo/UserInfo.php
@@ -16,15 +16,10 @@
 class UserInfo extends AuthorizedResourceBase
 {
 
-    /**
-     * @var \zaporylie\Vipps\Resource\HttpMethod
-     */
-    protected $method = HttpMethod::GET;
-
     /**
      * @var string
      */
-    protected $path = '/vipps-userinfo-api/userinfo/{id}';
+    protected string $path = '/vipps-userinfo-api/userinfo/{id}';
 
     /**
      * AbstractResource constructor.
@@ -42,6 +37,7 @@ public function __construct(VippsInterface $vipps, $sub)
             $this->app->getClient()->getTokenStorage()->get()->getTokenType()
             .' '.
             $this->app->getClient()->getTokenStorage()->get()->getAccessToken();
+        $this->method = HttpMethod::GET();
     }
 
     /**
diff --git a/src/Vipps.php b/src/Vipps.php
index 98f6fb5..dcace5b 100644
--- a/src/Vipps.php
+++ b/src/Vipps.php
@@ -9,9 +9,13 @@
 namespace zaporylie\Vipps;
 
 use zaporylie\Vipps\Api\Authorization;
+use zaporylie\Vipps\Api\AuthorizationInterface;
 use zaporylie\Vipps\Api\Payment;
+use zaporylie\Vipps\Api\PaymentInterface;
 use zaporylie\Vipps\Api\RecurringPayment;
+use zaporylie\Vipps\Api\RecurringPaymentInterface;
 use zaporylie\Vipps\Api\UserInfo;
+use zaporylie\Vipps\Api\UserInfoInterface;
 
 /**
  * Class Vipps
@@ -23,7 +27,7 @@ class Vipps implements VippsInterface
     /**
      * @var \zaporylie\Vipps\ClientInterface
      */
-    protected $client;
+    protected ClientInterface $client;
 
     /**
      * Vipps constructor.
@@ -38,7 +42,7 @@ public function __construct(ClientInterface $client)
     /**
      * {@inheritdoc}
      */
-    public function getClient()
+    public function getClient(): ClientInterface
     {
         return $this->client;
     }
@@ -48,9 +52,9 @@ public function getClient()
      * @param string $merchant_serial_number
      * @param string $custom_path
      *
-     * @return \zaporylie\Vipps\Api\Payment
+     * @return \zaporylie\Vipps\Api\PaymentInterface
      */
-    public function payment($subscription_key, $merchant_serial_number, $custom_path = 'ecomm')
+    public function payment(string $subscription_key, string $merchant_serial_number, string $custom_path = 'ecomm'): PaymentInterface
     {
         return new Payment($this, $subscription_key, $merchant_serial_number, $custom_path);
     }
@@ -61,7 +65,7 @@ public function payment($subscription_key, $merchant_serial_number, $custom_path
      *
      * @return \zaporylie\Vipps\Api\RecurringPaymentInterface
      */
-    public function recurringPayment($subscription_key, $merchant_serial_number)
+    public function recurringPayment(string $subscription_key, string $merchant_serial_number): RecurringPaymentInterface
     {
         return new RecurringPayment($this, $subscription_key, $merchant_serial_number);
     }
@@ -69,7 +73,7 @@ public function recurringPayment($subscription_key, $merchant_serial_number)
     /**
      * @return \zaporylie\Vipps\Api\UserInfoInterface
      */
-    public function userInfo()
+    public function userInfo(): UserInfoInterface
     {
         return new UserInfo($this);
     }
@@ -77,9 +81,9 @@ public function userInfo()
     /**
      * @param string $subscription_key
      *
-     * @return \zaporylie\Vipps\Api\Authorization
+     * @return \zaporylie\Vipps\Api\AuthorizationInterface
      */
-    public function authorization($subscription_key)
+    public function authorization(string $subscription_key): AuthorizationInterface
     {
         return new Authorization($this, $subscription_key);
     }
diff --git a/src/VippsInterface.php b/src/VippsInterface.php
index 60ec7d5..50cffab 100644
--- a/src/VippsInterface.php
+++ b/src/VippsInterface.php
@@ -8,8 +8,14 @@
 
 namespace zaporylie\Vipps;
 
+use zaporylie\Vipps\Api\AuthorizationInterface;
+use zaporylie\Vipps\Api\PaymentInterface;
+use zaporylie\Vipps\Api\RecurringPaymentInterface;
+use zaporylie\Vipps\Api\UserInfoInterface;
+
 /**
  * Interface VippsInterface
+ *
  * @package Vipps
  */
 interface VippsInterface
@@ -18,14 +24,19 @@ interface VippsInterface
     /**
      * @return \zaporylie\Vipps\ClientInterface
      */
-    public function getClient();
+    public function getClient(): ClientInterface;
 
     /**
      * @param string $subscription_key
      *
      * @return \zaporylie\Vipps\Api\AuthorizationInterface
      */
-    public function authorization($subscription_key);
+    public function authorization(string $subscription_key): AuthorizationInterface;
+
+    /**
+     * @return \zaporylie\Vipps\UserInfoInterface
+     */
+    public function userInfo(): UserInfoInterface;
 
     /**
      * @param string $subscription_key
@@ -34,7 +45,7 @@ public function authorization($subscription_key);
      *
      * @return \zaporylie\Vipps\Api\PaymentInterface
      */
-    public function payment($subscription_key, $merchant_serial_number, $custom_path);
+    public function payment(string $subscription_key, string $merchant_serial_number, string $custom_path): PaymentInterface;
 
     /**
      * @param string $subscription_key
@@ -42,5 +53,5 @@ public function payment($subscription_key, $merchant_serial_number, $custom_path
      *
      * @return \zaporylie\Vipps\Api\RecurringPaymentInterface
      */
-    public function recurringPayment($subscription_key, $merchant_serial_number);
+    public function recurringPayment(string $subscription_key, string $merchant_serial_number): RecurringPaymentInterface;
 }
diff --git a/test/Unit/Api/ApiBaseTest.php b/test/Unit/Api/ApiBaseTest.php
index 14ad783..2197f6d 100644
--- a/test/Unit/Api/ApiBaseTest.php
+++ b/test/Unit/Api/ApiBaseTest.php
@@ -38,8 +38,5 @@ protected function setUp() : void
     public function testSubscriptionKey()
     {
         $this->assertEquals('test_subscription_key', $this->apiBase->getSubscriptionKey());
-        $this->assertInstanceOf(ApiBase::class, $this->apiBase->setSubscriptionKey(null));
-        $this->expectException(InvalidArgumentException::class);
-        $this->apiBase->getSubscriptionKey();
     }
 }
diff --git a/test/Unit/Api/PaymentTest.php b/test/Unit/Api/PaymentTest.php
index 862cb8d..e548624 100644
--- a/test/Unit/Api/PaymentTest.php
+++ b/test/Unit/Api/PaymentTest.php
@@ -21,9 +21,6 @@ public function testMerchantSerialNumber()
         $vipps = $this->createMock(Vipps::class);
         $api = new Payment($vipps, 'test_subscription_key', 'test_merchant_serial_number');
         $this->assertEquals('test_merchant_serial_number', $api->getMerchantSerialNumber());
-        $api = new Payment($vipps, 'test_subscription_key', null);
-        $this->expectException(InvalidArgumentException::class);
-        $api->getMerchantSerialNumber();
     }
 
     /**
diff --git a/test/Unit/Authentication/TestTokenStorage.php b/test/Unit/Authentication/TestTokenStorage.php
index e1711c1..ce2a30a 100644
--- a/test/Unit/Authentication/TestTokenStorage.php
+++ b/test/Unit/Authentication/TestTokenStorage.php
@@ -7,7 +7,7 @@
 
 class TestTokenStorage extends TokenMemoryCacheStorage
 {
-    public function get()
+    public function get(): ResponseGetToken
     {
         $token = new ResponseGetToken();
 
diff --git a/test/Unit/ClientTest.php b/test/Unit/ClientTest.php
index 50472f8..4c3619a 100644
--- a/test/Unit/ClientTest.php
+++ b/test/Unit/ClientTest.php
@@ -42,9 +42,6 @@ protected function setUp() : void
     public function testClientId()
     {
         $this->assertEquals('test', $this->client->getClientId());
-        $this->assertInstanceOf(ClientInterface::class, $this->client->setClientId(null));
-        $this->expectException(InvalidArgumentException::class);
-        $this->client->getClientId();
     }
 
     /**
diff --git a/test/Unit/Model/UserInfo/AccountInfoTest.php b/test/Unit/Model/UserInfo/AccountInfoTest.php
new file mode 100644
index 0000000..1acebe2
--- /dev/null
+++ b/test/Unit/Model/UserInfo/AccountInfoTest.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace zaporylie\Vipps\Tests\Unit\Model\UserInfo;
+
+use JMS\Serializer\SerializerBuilder;
+use zaporylie\Vipps\Model\UserInfo\AccountInfo;
+use zaporylie\Vipps\Tests\Unit\Model\ModelTestBase;
+
+class AccountInfoTest extends ModelTestBase
+{
+
+    /**
+     * @var \zaporylie\Vipps\Model\UserInfo\AccountInfo
+     */
+    protected $model;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setUp() : void
+    {
+        parent::setUp();
+        $data = [
+            "account_name" => "Savings account",
+            "account_number" => 86011117947,
+            "bank_name" => "ACME Bank"
+        ];
+        $serializer = SerializerBuilder::create()->build();
+        $this->model = $serializer->deserialize(json_encode($data), AccountInfo::class, 'json');
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\AccountInfo::getAccountName()
+     */
+    public function testGetAccountName()
+    {
+        $this->assertEquals('Savings account', $this->model->getAccountName());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\AccountInfo::getAccountNumber()
+     */
+    public function testGetAccountNumber()
+    {
+        $this->assertEquals(86011117947, $this->model->getAccountNumber());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\AccountInfo::getBankName()
+     */
+    public function testGetBankName()
+    {
+        $this->assertEquals('ACME Bank', $this->model->getBankName());
+    }
+}
diff --git a/test/Unit/Model/UserInfo/AddressTest.php b/test/Unit/Model/UserInfo/AddressTest.php
new file mode 100644
index 0000000..1d2fa4f
--- /dev/null
+++ b/test/Unit/Model/UserInfo/AddressTest.php
@@ -0,0 +1,84 @@
+<?php
+
+namespace zaporylie\Vipps\Tests\Unit\Model\UserInfo;
+
+use JMS\Serializer\SerializerBuilder;
+use zaporylie\Vipps\Model\UserInfo\AccountInfo;
+use zaporylie\Vipps\Model\UserInfo\Address;
+use zaporylie\Vipps\Tests\Unit\Model\ModelTestBase;
+
+class AddressTest extends ModelTestBase
+{
+
+    /**
+     * @var \zaporylie\Vipps\Model\UserInfo\Address
+     */
+    protected $model;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setUp() : void
+    {
+        parent::setUp();
+        $data = [
+            "address_type" => "home",
+            "country" => "NO",
+            "default" => true,
+            "formatted" => "Robert Levins gate 5\n0154 Oslo",
+            "postal_code" => "0154",
+            "region" => "Oslo",
+            "street_address" => "Robert Levins gate 5"
+        ];
+        $serializer = SerializerBuilder::create()->build();
+        $this->model = $serializer->deserialize(json_encode($data), Address::class, 'json');
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\Address::getAddressType()
+     */
+    public function testGetAddressType()
+    {
+        $this->assertEquals('home', $this->model->getAddressType());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\Address::getCountry
+     */
+    public function testGetCountry()
+    {
+        $this->assertEquals('NO', $this->model->getCountry());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\Address::getFormatted
+     */
+    public function testGetFormatted()
+    {
+        $this->assertEquals("Robert Levins gate 5\n0154 Oslo", $this->model->getFormatted());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\Address::getPostalCode
+     */
+    public function testGetPostalCode()
+    {
+        $this->assertEquals('0154', $this->model->getPostalCode());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\Address::getRegion
+     */
+    public function testGetRegion()
+    {
+        $this->assertEquals('Oslo', $this->model->getRegion());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\Address::getStreetAddress
+     */
+    public function testGetStreetAddress()
+    {
+        $this->assertEquals('Robert Levins gate 5', $this->model->getStreetAddress());
+    }
+}
diff --git a/test/Unit/Model/UserInfo/ResponseUserInfoTest.php b/test/Unit/Model/UserInfo/ResponseUserInfoTest.php
new file mode 100644
index 0000000..c871a8c
--- /dev/null
+++ b/test/Unit/Model/UserInfo/ResponseUserInfoTest.php
@@ -0,0 +1,166 @@
+<?php
+
+namespace zaporylie\Vipps\Tests\Unit\Model\UserInfo;
+
+use zaporylie\Vipps\Model\Payment\ResponseGetOrderStatus;
+use zaporylie\Vipps\Model\Payment\TransactionInfo;
+use zaporylie\Vipps\Model\UserInfo\Address;
+use zaporylie\Vipps\Model\UserInfo\ResponseUserInfo;
+use zaporylie\Vipps\Resource\Payment\GetOrderStatus;
+use zaporylie\Vipps\Resource\UserInfo\UserInfo;
+use zaporylie\Vipps\Tests\Unit\Model\ModelTestBase;
+
+class ResponseUserInfoTest extends ModelTestBase
+{
+
+    /**
+     * @var \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo
+     */
+    protected $model;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setUp() : void
+    {
+        parent::setUp();
+        $resource = new UserInfo($this->vipps, 'test');
+        $this->model = $resource->getSerializer()->deserialize(
+            json_encode((object) [
+                "accounts" => [[
+                    "account_name" => "Savings account",
+                    "account_number" => 86011117947,
+                    "bank_name" => "ACME Bank"
+                ]],
+                "address" => [
+                    "address_type" => "home",
+                    "country" => "NO",
+                    "default" => true,
+                    "formatted" => "Robert Levins gate 5\n0154 Oslo",
+                    "postal_code" => "0154",
+                    "region" => "Oslo",
+                    "street_address" => "Robert Levins gate 5"
+                ],
+                "other_addresses" => [[
+                    "address_type" => "home",
+                    "country" => "NO",
+                    "default" => true,
+                    "formatted" => "Robert Levins gate 5\n0154 Oslo",
+                    "postal_code" => "0154",
+                    "region" => "Oslo",
+                    "street_address" => "Robert Levins gate 5"
+                ]],
+                "birthdate" => "2000-12-31",
+                "email" => "user@example.com",
+                "email_verified" => true,
+                "family_name" => "Lovelace",
+                "given_name" => "Ada",
+                "name" => "Ada Lovelace",
+                "nin" => "09057517287",
+                "phone_number" => "47912345678",
+                "sid" => "7d78a726-af92-499e-b857-de263ef9a969",
+                "sub" => "c06c4afe-d9e1-4c5d-939a-177d752a0944"
+            ]),
+            ResponseUserInfo::class,
+            'json'
+        );
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getAccounts
+     */
+    public function testGetAccounts()
+    {
+        $this->assertIsArray($this->model->getAccounts());
+        $this->assertNotEmpty($this->model->getAccounts());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getAddress
+     */
+    public function testGetAddress()
+    {
+        $this->assertInstanceOf(Address::class, $this->model->getAddress());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getBirthdate
+     */
+    public function testGetBirthday()
+    {
+        $this->assertEquals('2000-12-31', $this->model->getBirthdate());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getEmail
+     */
+    public function testGetEmail()
+    {
+        $this->assertEquals('user@example.com', $this->model->getEmail());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getFamilyName
+     */
+    public function testGetFamilyName()
+    {
+        $this->assertEquals('Lovelace', $this->model->getFamilyName());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getGivenName
+     */
+    public function testGetGivenName()
+    {
+        $this->assertEquals('Ada', $this->model->getGivenName());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getName
+     */
+    public function testGetName()
+    {
+        $this->assertEquals('Ada Lovelace', $this->model->getName());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getNin
+     */
+    public function testGetNin()
+    {
+        $this->assertEquals('09057517287', $this->model->getNin());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getPhoneNumber
+     */
+    public function testGetPhoneNumber()
+    {
+        $this->assertEquals('47912345678', $this->model->getPhoneNumber());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getSid
+     */
+    public function testGetSid()
+    {
+        $this->assertEquals('7d78a726-af92-499e-b857-de263ef9a969', $this->model->getSid());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getSub
+     */
+    public function testGetSub()
+    {
+        $this->assertEquals('c06c4afe-d9e1-4c5d-939a-177d752a0944', $this->model->getSub());
+    }
+
+    /**
+     * @covers \zaporylie\Vipps\Model\UserInfo\ResponseUserInfo::getOtherAddresses
+     */
+    public function testGetOtherAddresses()
+    {
+        $this->assertIsArray($this->model->getOtherAddresses());
+        $this->assertNotEmpty($this->model->getOtherAddresses());
+    }
+}
diff --git a/test/Unit/Resource/ResourceBaseTest.php b/test/Unit/Resource/ResourceBaseTest.php
index 1b58d26..5db6a39 100644
--- a/test/Unit/Resource/ResourceBaseTest.php
+++ b/test/Unit/Resource/ResourceBaseTest.php
@@ -40,7 +40,7 @@ protected function setUp() : void
         $reflection = new \ReflectionClass($this->resourceBase);
         $method = $reflection->getProperty('method');
         $method->setAccessible(true);
-        $method->setValue($this->resourceBase, HttpMethod::POST);
+        $method->setValue($this->resourceBase, HttpMethod::POST());
 
         // Set default body.
         $body = $reflection->getProperty('body');
@@ -87,10 +87,8 @@ public function testMethod()
         $reflection = new \ReflectionClass($this->resourceBase);
         $method = $reflection->getProperty('method');
         $method->setAccessible(true);
+        $this->expectError();
         $method->setValue($this->resourceBase, null);
-
-        $this->expectException(\LogicException::class);
-        $this->resourceBase->getMethod();
     }
 
     /**
@@ -103,10 +101,8 @@ public function testPath()
         $reflection = new \ReflectionClass($this->resourceBase);
         $path = $reflection->getProperty('path');
         $path->setAccessible(true);
+        $this->expectError();
         $path->setValue($this->resourceBase, null);
-
-        $this->expectException(\LogicException::class);
-        $this->resourceBase->getPath();
     }
 
     /**