Unable to create application perspectives

[JohnEllwoodNHS]

Using the latest version of the Instana provider (4.0.0) I am unable to create an application perspective, even using the example in the docs:

resource "instana_application_config" "example" {
  label               = "label"
  scope               = "INCLUDE_ALL_DOWNSTREAM"  #Optional, default = INCLUDE_NO_DOWNSTREAM
  boundary_scope      = "INBOUND"  #Optional, default = INBOUND
  tag_filter          = "agent.tag:stage EQUALS 'test' OR aws.ec2.tag:stage EQUALS 'test' OR call.tag:stage@na EQUALS 'test'"
}

The response is always a 500 error:

 Error: failed to send HTTP PUT request to Instana API; status code = 500; status message = 500 Internal Server Error; 
│ Body: {"errors":["Unexpected error during request processing"]}
│
│   with instana_application_config.example,
│   on example_application_perspective.tf line 1, in resource "instana_application_config" "example":
│    1: resource "instana_application_config" "example" {
│

TF for other resources such as events and alerts are working fine. The API key in use has full permissions to manage all resource types.

Curling the endpoint works:

curl -X POST -H "authorization: apiToken ****************" -H "Content-Type: application/json"  https://**********-********.instana.io/api/application-monitoring/settings/application -d '{
  "label": "example",
  "tagFilterExpression": {
    "type": "EXPRESSION",
    "logicalOperator": "OR",
    "elements": [
      {
        "type": "TAG_FILTER",
        "name": "kubernetes.namespace.name",
        "operator": "EQUALS",
        "value": "example",
        "entity": "DESTINATION"
      }
    ]
  }
}'

.... but what I believe is the equivalent TF fails:

resource "instana_application_config" "example" {
  label               = "label"
  tag_filter          = "kubernetes.namespace.name EQUALS 'example'"
}