Can't connect Frsky R9Slim Receiver to Ardupilot

Hi guys.

I’m having trouble connecting my receiver to Ardupilot.

The FC (Flight Controller) I’m using is a Mamba F405 MK2.
The receiver is a Frsky R9 Slim.
The transmitter is a Frsky X Lite with a R9M lite.

I currently have the R9Slim S-Port connected to FC in the S-Bus port. The receiver flashes green so I suspect the problem is somewhere in the interface of the receiver with Ardupilot or/and the FC.

On Ardupilot I have the following parameters set to:
RC-options: 32
RC-override_time: 3
RC-protocols: 8 (This sets it to Sbus, I think)
RC-speed: 490 Hz

Does anyone have any idea of what might be happening?

Thank you,