Same issue over here. developer AT example.com got kicked. I changed the Apple-ID to jan.developer AT example.com and then it was accepted. Gmail users can add dots anywhere in the own name, so they should be able to do the same. But users at other domains might not have the same flexibility.

The release notes of 14.3.1 do not mention iOS 16.5, but if you try it support is there.

The code examples in that guide are for Swift. What to do if your app still is pure Objective-C?