These 9XR radios are pretty popular because they are cheap and have lots of features, which is attractive to newbies and veterans alike. But they are not "plug and play", they have setup menus that are daunting. This would also apply to a 9X, Taranis or TH9X...maybe other radios with ER9X or OpenTX.
I have the menu's for a 9XR with PPM receiver (Rangelink) to an APM. This diagram is for an ArduCopter setup. At my site I have further explanation and ArduPlane setup details.