Specifically, in what standard format are the parameters passed? Using Json? Http headers? Encoded onto the Uri? What? A tangible example of the exact HTTP POST request sent from the client, byte by byte, would have been enormously helpful here. As is now, I'm blind on the server side - I don't know what data to expect and have to guess how the client sends its data?
If you go here :
http://bitid.bitcoin.blue/loginAnd click on "manual", you'll get a curl example showing exactly how to POST on the demo server implementation.