Good day @herbstdr,
The order of the PPM encoder's cables by color with the receivers we use is (CH1, CH2...) signal, orange, yellow, green, blue and grey. From what I see the grey one isn't connected and the signal connector (black, red and white) seems to be connected to the sixth channel, that might be part of your problem. The channel order should be the one I just said, but the signal input might be different in that receptor, maybe you are just lacking the grey connector? I'd connect it and check, if it still doesn't work, I'd connect the signal one first then the rest in the same order.
You should be able to check for input in a more convenient way with any GCS software like APM Planner 2.
I'm sorry to say we don't give support for hardware we don't provide.