I get "Bad channel 1 input" when trying to calibrate radio

I’m still trying to find an answer to this, 3DR support hasn’t been helpful so far.

Basically, my Iris+ isn’t getting commands from my radio controller, the box with the joysticks and the FrSky DJT. Mission Planner thinks the controller isn’t turned on, even though it’s bound to the D4R-II receiver, and the controller is getting data like altitude, satellites, battery voltage, etc.

When I try to calibrate the radio with Mission Planner, I get no green in the UI, where it’s supposed to have green bars that indicate the positions of the controls, and in the end I get this message “Bad channel 1 input, cancelling”.

Can anyone shed some light on what needs to be replaced?