+1 and yes, I am naive enough to expect it to work in XCode 13 and iOS 15 sim

Quite an old question, but I'll try to answer it for others even if OP have already figured it out. There is no code of requesting the sign-in flow posted, so I'll just assume that OP combined 2 types of request like it is described in Documentation let requests = [ASAuthorizationAppleIDProvider().createRequest(), ASAuthorizationPasswordProvider().createRequest()] Doing this results in no authorizationCode being returned (or actually returned as nil) in ASAuthorizationAppleIDCredential As for why this happens? Good question I do not know the answer yet.

I have this issue with my usual AppleID credentials - they were listed in Sandbox iOS Settings and I successfully performed sandboxed purchase (note - this apple id is not listed in Sandbox Testers list in App Store Connect). I have no issue (not yet at least) with another dummy AppleID that I have created via Sandbox Testers page.