Face ID isn’t working what do I need to do
Face ID not working
iPhone X, iOS 12
The vast majority of the time if your FaceID isn't working you simply need to Shut Down your iPhone and turn it back on normally. You can go to Settings > General and swipe all the way to the very very button and select Shut Down.
If that hasn't cured it bring up your Camera App and switch to your front-facing camera to make sure that even works for normal pictures. If it doesn't, you'll need hardware service.
You can call or chat into AppleCare's 24/7 chat support and they can run a remote diagnostics to see if that detects a failure. But whether it affirmatively detects a problem or not, you will need to get service on it.
If you are lucky, your iPhone X may be covered for this issue outside of warranty:
https://www.apple.com/support/iphone-x-display-module-replacement-program/
