I've had that message pop up when I open my tailgate with trailer connected . After i clear message all is ok . Maybe a connection near tailgate/spare tire?
I wired in led brake and tail bulbs to simulate a trailer hook up and plugged them into a curt 55384 4 pin adaptor. You also have to enable the feature in the settings.
i wired in some led lights for turn and brake to simulate a trailer being hooked up . It thinks you have a trailer and then turn signals activate camera no need to push tow/haul button