Face ID is not working on my iPhone

If Face ID isn't working for you, there is most likely something wrong with your TrueDepth camera. First, look at these two articles for help. If that doesn't fix the issue, then make an appointment at the Genius Bar to have your camera issue diagnosed.

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

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

Make an appointment at the Genius Bar to have it diagnosed.

Genius Bar Reservation and Apple Support Options - Apple

did you try turning it off and on again