Failed—unable to complete Touch ID setup. What should I do please?

If you're using a case or screen protector, make sure it doesn't cover the Touch ID sensor or the surrounding ring. Go to Settings > Touch ID & Passcode and make sure that iPhone Unlock or iTunes & App Store is on, and that you've enrolled one or more fingerprints. Try enrolling a different finger.

If Touch ID isn't working on your iPhone or iPad - Apple Support