Add Teams Chat Member API call inexplicably Failing

I have tried every possible permutation of this API call that I can imagine. Nothing works. I already started a thread on this, but now it appears to be glitched and I can no longer reply to message sin that thread for some reason. What can I do to contact Microsoft Support and speak directly to their API team? The responses I have gotten all appear to be AI generated and NONE ARE CORRECT.  I really need help, from a human, that actually might understand what's going on here. Please help.

"#microsoft.graph.aadUserConversationMember' for 'odata.type' is not valid for this operation." <- I am receiving this error despite the fact that we already have several users in this channel with that same type.

This API call is intended to invite a user to an existing group chat. This should really be a very simple thing.

 1. ALL users in the group chat already have type = '#microsoft.graph.aadUserConversationMember' so the error message doesn't even make sense.
2. This IS a Group chat. NOT a channel. NOT a one on one chat. 
3. The Inviter has permission to invite users to this groupchat through the frontend. (and in fact can do so using the frontend.)

Why is this API call failing? I have tried scrubbing the API call of special characters, I have tried using the beta endpoint, I have tried several different formats for the input.

ERROR: 

{"error":{"code":"BadRequest","message":"The provided '#microsoft.graph.aadUserConversationMember' for 'odata.type' is not valid for this operation.","innerError":{"date":"2026-02-10T19:11:28","request-id":"XXXXX","client-request-id":"XXXXXX"}}}

POST

URL: https://graph.microsoft.com/v1.0/chats/IDHERE/members

BODY:
{

"chatType": "group",

"\u0040odata.type": "#microsoft.graph.aadUserConversationMember",

"user\u0040odata.bind": "https://graph.microsoft.com/v1.0/users/IDHERE",

"roles": []

}