I had this question after I just updated to the latest version of iPhone and I just got it resolved! ( sorry you may have already resolved the problem, but I hope this will be useful to the newbies, like me).
you need to TURN OFF the two factor authentification
- Sign in to https://appleid.apple.com
- Scroll to security ( now here they make it look like you can’t turn it off) and click edit
- Click “turn-off Two-Factor authentication” then confirm and click done
- It will ask you to set up new security questions, and blablabla - THEN YOU ARE SAVED!
I have pictures on how to perform the steps on my blog, which is my username followed by a dot com.