My Face ID isn't working

Have a look at these two articles -

If an alert says Face ID has been disabled on your iPhone or iPad Pro

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

If Face ID isn't working on your iPhone.

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

Try to update your iPhone to the latest iOS version. If this is not working, please contact apple support to set your device up for service