HTTP 415 - Unsupported Media Type with proper content type

[#1]

Hi everyone!

Apigee is sending 415 response for any POST request, and I'm having hard time to debug what is going wrong. I'm passing Content-Type: application/json as suggested in related question, but it doesn't make any difference. In the same time, if I set content type to multipart-form, Apigee consider it as valid request, but body of that request becomes empty.

Is there a way to get some insights why it is happening?

What Apigee consider as supported content type?

Is there a way to tell Apigee which content type is correct?

Sample of my request:

{
  "method": "POST",
  "url": "https://<host>/v1/auth",
  "headers": {
    "ApiKey": "<apikey>",
    "Content-Type": "application/json",
    "Accept": "application/json"
  },
  "data": "{\"accountId\": 1}"
}

Sample of response:

{
  "pragma": "no-cache",
  "date": "Wed, 14 Feb 2018 15:15:11 GMT",
  "cache-control": "no-cache",
  "connection": "close",
  "content-length": "18",
  "content-type": "text/plain",
  "status": 415
}