curl --request POST \
  --url https://{defaultHost}/v1/apps/{app_id}/message_service_providers \
  --header 'Authorization: Bearer <token>' \
  --header 'X-Authorization: <api-key>'

{
  "message_service_provider": {
    "provider_type": "<string>",
    "config": {},
    "enabled": true,
    "name": "<string>"
  }
}