“My Pixhawk 6C and RadioMaster RP3 receiver are failing to communicate. The receiver is successfully bound to the radio, and the RP3 is connected to the TELEM2 port. I have configured the relevant port to RCIN and am running ArduPilot firmware v4.6.3. However, the ground station (Mission Planner/QGC) cannot detect the radio input, and the calibration page remains greyed out. Does anyone know how to fix this?”
Your information is not showing any details abourt your connection and your configuration.
So show detailed interconnection diagram pin by pin and all your PARAMS first