place-order.php

<?php
require_once 'api.php';

// The URL to your Magento 2 instance (ending with /index.php/rest/V1)
$api_url = 'http://your-domain.com/index.php/rest/V1';
// Set the integrations access token.
$token = 'your_access_token';
// Fill in the SKU of the product which should be ordered.
$sku = '24-WB04';

$magento = new MagentoClient($token, $api_url);

if (isset($_GET['cartId']) && !empty($_GET['cartId']))
{
  $cart = $_GET['cartId'];
}
else
{
  $cart = $magento->createCart();
  $cart = str_replace('"', '', $cart);
  $order_filled = $magento->addToCart($cart, $sku, 1);

  // var_dump($order_filled);

  $ship_to = array (
    'addressInformation' =>
      array (
        'shippingAddress' =>
          array (
            'region' => 'Wien',
            'region_id' => 95,
            'country_id' => 'AT',
            'street' =>
              array (
                0 => 'Fillgradergasse 12-14/1a',
              ),
            'company' => 'acolono GmbH',
            'telephone' => '1111111',
            'postcode' => '1060',
            'city' => 'Vienna',
            'firstname' => 'Martin',
            'lastname' => 'Testman',
            'email' => 'testman@acolono.com',
            'prefix' => 'address_',
            'region_code' => 'W',
            'sameAsBilling' => 1,
          ),
        'billingAddress' =>
          array (
            'region' => 'Wien',
            'region_id' => 95,
            'country_id' => 'AT',
            'street' =>
              array (
                0 => 'Fillgradergasse 12-14/1a',
              ),
            'company' => 'acolono GmbH',
            'telephone' => '1111111',
            'postcode' => '1060',
            'city' => 'Vienna',
            'firstname' => 'Martin',
            'lastname' => 'Testman',
            'email' => 'testman@acolono.com',
            'prefix' => 'address_',
            'region_code' => 'W',
          ),
        'shipping_method_code' => 'flatrate',
        'shipping_carrier_code' => 'flatrate',
      ),
  );

  $order_shipment = $magento->setShipping($cart, $ship_to);
  // var_dump($order_shipment);
  if(!defined('STDIN'))
  {
    echo json_encode(["cartId" => $cart]);
    return;
  }
}

//$payment = $magento->getPaymentMethods($cart);
//var_dump($payment);

$additionalData = [
    "cc_stripejs_token" => "pm_card_visa" // Use pm_card_threeDSecureRequired for 3D Secure authentication
];

$ordered = $magento->placeOrder($cart, 'stripe_payments', $additionalData);
echo "Order ID: $ordered";