iPhone camera is not recognized “unknown part”

My camera one night started lagging and it was just a black screen, I restarted my phone and a few hours later on my Home Screen I got a message stating camera is not recognized and that a service provider needs to fix it. Mind you I did nothing to the camera it just happened randomly. I talked to Apple yesterday for an hour and they basically said I’d have to pay for it which I don’t think is fair considering this message is basically saying my camera is not a genuine part of my phone. They also said if I trade it in it will diminish the value since I need to fix the camera. I tried to reset my phone settings because others said that works and I updated my phone but the message is still there. Anyone know how to fix it without having to take it in?