Face ID is not working on iPhone

Here is what to do: If Face ID isn't working on your iPhone or iPad Pro - Apple Support

If that fails to get Face ID working, you'll want to discuss your options and alternatives with Apple Support: Support

There may be something wrong with your TrueDepth camera. Please review the following articles. 

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

If an alert says Face ID has an issue on your iPhone or iPad Pro - Apple Support

If the above doesn’t help, please make a reservation at your nearest Apple Store Genius Bar or Apple Authorized Service Provider for diagnostics. 

Genius Bar Reservation and Apple Support Options - Apple