Examine the exterior part of the camera and cable,
Check if the rear port on the front and rear cam is faulty or not,
if the rear cable looks good,
Check the setting in the cam,
Please unplug and replug the rear cable again carefully.
check the Live Video Source and check if the rear cam is grayed out,
If unfortunately the rear cam is still not detected, you may need a new rear cable as the first solution.
Contact customer service if the issue persists.
Note: A129 PLUS use a different rear cam with A129 Duo and PRO