Here is some of what it says.

– Face ID will not work in the battery saving mode. If your phone is at 10% battery power or less, entering password will be the only way to unlock it,
– for the same reason, Apple Pay will not work with Face ID when the battery is low,
– Face ID will not work after restarting the phone,
– smartphone must be unlocked at least once every 48 hours, otherwise, you guessed it, FaceID will not work,
– system will lock itself after five faild attempts at facial recognition,
– sunglasses may, but do not have to, cause issues with facial recognition,BR>- phone’s password must be entered at least once every six and a half day, otherwise it will lock. Why? Who knows.