That’s a closure

Sounds like you should respond to that with a 400 Bad Request

The server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

When you aren't feeling that async energy but you still get a callback.

And then in the call you end up discussing what to put in the mail for "awareness"