RPM reading on Pixhawk 6x with ICE


recently bought Pixhawk 6x, flashed Arducopter heli 4.3.5 firmware into it with no issues. Got through all the basic setup and calibration. Now to the issue, my UAV is a rather large traditional helicopter with internal combustion engine, so I need to read RPM. Did all the configuration as is said in the documentation, but I never get any RPM readings. When I plot RPM1 and RPM2 in MissionPlanner, it always says -1, which I don’t know the meaning of. I can’t find anywhere what -1 RPM reading means.

I only use RPM1, type is set to GPIO, RPMPIN is set to Aux6. I never get any RPM reading. Tried different aux pins as well, RPM2 too, but no success.

I saw in the documentation this line “Everytime the autopilot initializes, it sends a log message to the ground control station, showing which outputs are PWM/Oneshot/or DShot. The remaining higher numbered outputs are assigned as GPIOs.”

In my case it says this - 18/03/2023 14:29:27 : RCOut: PWM:1-16

I don’t know what I could be doing wrong, if I’m missing some setting, anyone got any ideas?

Thanks in advance!