It seems my Transmitter is bound to the receiver, but I still can't arm the motors?
To verify what other Pre-Arm safety check are preventing you from continuing, you can connect your IRIS+ to Mission Planner on your PC.
In the ''FLIGHT DATA'' Tab, under the horizon window, click on the ''Actions'' Tab.
There you'll see an Icon labeled ''Arm/Disarm''. Now, before clicking it, please note that the motors may spin at this point so if you have propellers on, you may want to remove them for safety reasons.
Click it. If you still weren't able to arm the motors this way, you should have received a message in the Horizon window telling you what Pre-Arm check is being activated.
If it's because of calibrations, you can correct this in the ''INITIAL SETUP'' Tab, under ''Mandatory Hardware'' by going through the indicated calibration procedure.