I've been struggling to get an Adafruit RFM96 module to work with your code. One issue appears to be with the sync word 0X0F0F. Since RadioLib's RFM9x support is based on the SX127x, when you dropped support for the SX127x (issue 10), that also dropped support for the RFM9x family. May I suggest you update the documentation on Github and in your Communications Guide to reflect this fact.