My Face ID isn't working on my iPhone

Are you getting an error message, that FaceID has been disabled?

If yes, take a look at the troubleshooting mentioned in this related article:

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

If you're getting a message that Face ID is disabled, this is most likely a hardware issue. Please update your iPhone to the latest available software version and if this is not working, Contact - Official Apple Support to set up hardware service for your device.