case_channel_not_api
HTTP status: 422 (Unprocessable)
Title: Case not from the API
Cause
Only cases that came through the API can be written to as the contact. On other channels the contact writes by themselves.
How to fix it
Read detail in the response: it says what to change. Do not retry the same request unchanged.
Every error carries requestId and the Request-Id header. Send it when you write to support.