How do I configure and send a JSON response to an Oracle APEX/ORDS incoming post request?

I have configured my ORDS/APEX to receive an incoming Post request and can succesfully receive the incoming JSON data.

After the data has been processed, the client wants a response JSON file as a response!
When testing in Postman, it seems like a response is being generated in JSON format. However, the client's system is unable to receive a response though they seem to have configured.

There was one odd case when the client did receive a JSON response of a successful transaction, but we were neither able to understand why/how or recreate it!