Why my Face ID is not working

Check this link...

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

If that link doesn't help, you will need to make an appointment at the nearest Apple Store for a repair...

Apple Store - Find a Store - Apple

There are many reasons for it. Maybe you have not yet verified through email and phone number. It is also possible that your browser is causing issue becuase sometimes cache makes problem in logging in. So try to clear cache and verify your ID.

Did you click on the first link in blue letters in my post above? If not, do so and you will find instructions that may help. If they do not help, you will need to click on the other link to find an Apple Store near you and you will need to make an appointment for a repair.

Well face id only works in latest iphone like iphone X and later on

you can try resetting your face id and check again or try restarting your iphone.

hope that helps