Face ID stop working

If you still need help, reset your Face ID, then set it up again. Go to Settings, tap Face ID & Passcode, then tap Reset Face ID. Next, tap Set up Face ID to set it up again.

If Face ID isn't working on your iPhone or iPad Pro

Hello,

Apple has several documents helping you with Face ID.

This Support article is specific to seeing a 'disabled' Face ID alert, and explains what to do when you see that notice or an issue with the TrueDepth camera. --> If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support

Unless a software update solves the problem you may need to have Apple take a look at your device. Use this link to set up an appointment —> Genius Bar Reservation and Apple Support Options - Apple and this one to get a repair estimate —> iPhone Repair & Service - Apple Support

If you don't see a 'disabled' message but do have general issues with Face ID not working properly, explore the list of things to try in this document: If Face ID isn't working on your iPhone or iPad Pro - Apple Support

If the first 8 don't solve the issue then use #9, contact Apple.