Suddenly my Face ID doesn’t work

If Face ID isn't working for you, there is most likely something wrong with your TrueDepth camera. First, look at these two articles for help. If that doesn't fix the issue, then make an appointment at the Genius Bar to have your camera issue diagnosed.

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

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

Make an appointment at the Genius Bar to have it diagnosed.

Genius Bar Reservation and Apple Support Options - Apple

For general issues with Face ID not working properly, explore the list in this article of things to try: If Face ID isn't working on your iPhone or iPad Pro - Apple Support

One person reported that simply cleaning the lens got Face ID working again —> Face ID stopped working and will not reset - Apple Community

Miscellaneous possible reasons for FaceID not working if none of the above apply: Face ID shows it's unavailable on my iPho… - Apple Community

Apple Support for Face ID not working as expected:

https://getsupport.apple.com/?caller=kbase&SG=SG003&category_id=SC0999&symptom_id=23303

or click on —> https://getsupport.apple.com/ , select iPhone, then scroll down to the contact methods.

This general description of how Face ID works, and security, may interest you --> About Face ID advanced technology - Apple Support

This article tells you how to add an alternate appearance -->

Set up Face ID on iPhone - Apple Support