iPhone Face ID Not Working
If Face ID suddenly stops working, you can try to fix it yourself by doing the following.
First, ensure your iPhone’s front-facing camera and sensors are clean. If not, try using a lint-free cloth to wipe any dirt or sweat your iPhone might have.
Also, be sure you don’t have anything covering your face, like a face mask or hair, and that you’re looking directly at your iPhone, as sometimes that might cause it not to work.
If that doesn’t work, go to Settings > Face ID & Passcode. Enter your passcode and then tap on Reset Face ID. Try setting up Face ID again and see if that fixes the problem.