Sometimes they nerf it. If people replace the cameras or screen. They call it a safety feature, but it's often seen as an effort to undermine independent repair.

But that's just speculation, there could be infinite reasons why it's not working in your case. But if you bought it used or refurbished, it's probably some kind of software lock to the camera and it needs to be either the original camera that came with the phone or repaired by Apple so they can connect it m