Welcome to iRV2 .
B-i-L had the same issue when he picked up his 05 Tiffin, don't know the camera or monitor brand , but the salesman ( YES the salesman ) knew of the problem and switched wiring, or a switch , at the back of the monitor to correct the issue. He did say he switched wires.
Took about three mins.
If you have, or can download, a manual on the camera or monitor , could be the problem, and repair, might be covered in the troubleshooting guide.