No radio input detected from SBUS receiver

ArduCopter Copter 4.0
1

My transmitter is has been binded with my receiver, but in Mission Planner and Qgroundcontrol none of the inputs from my radio channels are detected. The receiver is using SBUS.

I have tried changing each of the serialx_protocol to RCIN, in turn and none resolved the issue.

I am using:
Receiver: Radiomaster R81
TX module: FrSky DJT
Flight controller : Diatone Mamba H743
Autopilot: Arducopter 4.2.3

I have wired the receiver to RX1 as shown in the Diatone Mamba instructions below:

image

2

Refer to the Ardupilot wiki for details about it’s implementation on specific flight controllers.
AC Mamba H743