Was getting a similar error where sign in with apple wasn't working (getting "Sign up not completed") Here's what randomly worked for me: https://developer.apple.com/forums/thread/789323?answerId=845919022#845919022

Uhhh I removed the "Sign in with Apple" capability from Xcode and it WORKED!!! It's still checked inside my developer account → Identifier → App ID capabilities.. but removing it from "Signing & Capabilities" tab in Xcode got rid of the "Sign up not completed" error and finally worked, user saved in my backend's DB and everything. Note: it also removed it from my entitlement file (com.apple.developer.applesignin key) so idk wth is going on. Someone try this and lmk you get similar results! And why this workaround makes sense

I've seen so many threads with this SAME issue with zero help... no fix... nothing - driving me crazy!! Did you ever find a fix? @Carter001 @Sangeethkumarkesavan @songbird

I've seen so many threads with this SAME issue with zero help... no fix... nothing - driving me crazy!! Did you ever find a fix? @Sangeethkumarkesavan