Pixhawk 4 mini with ppm receiver: no channel in QGC


I have a pixhawk 4 mini with a jumper r8 receiver.
The sbus output of the receiver is plugged into the ppm slot of the PH4mini.
Some images:


Unfortunately, I dont see any channels in QGC.
Do I need to change an additional setting?
My setup works if I plug it in RCIN, but I want to use that I/O for something else.


PS: I have use my setup with Ardupilot, so likely no faulty equipment :wink: