Radio calibration problem OBAL


We are trying to get ardupilot to work on a raspberry pi zero 2 w with OBALboard(not GY-91 version).
When we connect to Mission Planner and start Radio Calibration, nothing happens. The connections succeeds and the ardupilot version is detected but no green bars are visible at all…
We use a raspberry pi zero 2 w with buster and
Flysky FS-i6X i6X 10CH 2.4GHz AFHDS 2A RC Transmitter With FS-iA10B Receiver
We have measured the inputs on the raspberry with an oscilloscope and there is a signal. 20ms period with 1-2ms ~3.4v pulses depending on stick position. But still, nothing in mission planner.

We have tried both version 4.2.2 and 4.4.0, same problem.

Do you have any ideas or tips that we can try?

We have some screenshots etc if it helps