How to resolve 'Apple Watch verification failed' error during setup?

Bought my son an Apple Watch SE-3 cellular and can’t set it up. Once it pairs and tells me to log in it gives Verfication Failed an unknown error occurred. Seeing this has happened to a bunch of people on here but no answer how to fix it. 100% the correct password. I’ve tried resetting network settings, unpaired and turned phone off and on again dozens of times. Nothing works.

[Edited by Moderator]

Original Title: Apple Watch Verification Failed