Reasons for not working are:The camera is obstructed or unclean.Your face is hidden.Your iOS version is no longer supported.
When Face ID Doesn't Work, Here's What to Do
When Face ID Doesn't Work, Here's What to Do
– Ensure that nothing is in front of your face or camera. Face ID requires that your face is clearly visible to the camera.
– Make sure you're holding your iPhone in the right way. Face ID works on the iPad regardless of how you look at it, but it won't work on the iPhone unless it's in portrait (vertical) mode.
– Clean the front camera lens so that there is no dirt or oil.– Start your iPhone again. If physical fixes fail, a software reset may be necessary.
– Turn your phone off and on, and enter your passcode. Lock it and try using Face ID to open it again.– Go to settings, select face id, and select passcode and see whether it is in on position.
"Require Attention" should be turned off. To disable this feature, go to Settings, select Face ID & Passcode, scroll down to Require Attention for Face ID, and change the switch to off/white.
Face ID may require an upgrade to function properly. To check if a new operating system version is available, go to Settings and select General, click on Software Update.
– Once the software has been updated and installed, unlock using your passcode, lock the phone again, and then test Face ID.– If nothing works go to Apple's support page and begin a service request.