Touch ID has stopped working
(Touch ID) appears again. The "Touch ID" has stopped working
[Re-Titled by Moderator]
Here are the steps provided by Apple: If Touch ID isn't working on your iPhone or iPad - Apple Support
Failing that, contact the folks at Apple Support.
If this iPhone has had a third-party hardware repair prior to this Touch ID issue arising, check first with the provider that performed the previous repair.
