Some solutions are obvious and just require reading the manual, or checking connections. But some solutions are unexpected and weird.
This will document some of the more unusual problems that can mess up an RC setup
List of odd problems and solutions
SpeedyBee F405-Wing
No voltage on DJI 9V port - Bent ground pin needed straightening
No output on S8, no Soft Serial for S-Port function - Factory firmware bugs, upgrade to INAV 6.1.1
FrSKY GRX8
Receiver unable to enter bind mode - Push harder on the bind button
Kootai A505 J3 Cub won't initiate - Futaba FASST protocol uses REVERSED throttle channel
Skywalker X8 wings out of alignment.
Manufacturer glued the spar at the top of the channel in one wing and bottom of the channel in the other wing - Cut out spar and foam packing and re glue correctly.
Ardupilot ELRS connection won't work (FIMI Manta - Matek F405 VTOL)
SERIAL5 was set to CRSF (Parameter = 23) as well as SERIAL6 which prevented Rx connection.
Only SERIAL6 should be set to CRSF
