1. Go to setting- Advanced-type in password 8861(some could be 666888,1680 or 1688 according to different manufacture.)-choose soft reverse setting-switch then save and reboot
2.Some unit could be backup camera excitantion line should link two together.
3. Always try to ask for setting file for the company to check if it the setting issue that cause the problem.
How to import car setting.https://youtu.be/VxLcJWuVgNg