1. Face id is unavailable due to conflict between the apple system and the installed APP.
Workaround: Press Volume, press Volume down, then press and hold the power button until the Apple icon appears and let go.
2, due to knock and fall pressure, water or use loss resulting in damage to the face component, because the face component under the screen handset, easy to be infiltrated by water or sweat, fall is also easy to shake it. So the failure rate is high,
Face components include: light sensor, front image head, infrared image head, dot matrix image head. They are encrypted with the cpu, one of them is broken and cannot be replaced directly. It is repaired by decryption, chip transplantation, flying line, repair welding.
In this case, do you first rule out software conflict? You force a reboot, try the system, see if you can fix it? If it cannot be repaired, the condition must be replaced