Problem Connecting Spektrum AR620 to PixHawk4

I have a PixHawk4 and an AR620 Spektrum radio Ive tried a connection via the data channel only to learn that DSMX and the DSM2 channel do not work together.

so then on the advice of Holybro tech support I purchased a PPM encoder and have connected it into the PPM/RC channel but the QGroundControl says No Radio Detected.

Ive got a solid bind on the receiver and xmitter (tested it on other models)

when the Pixhawk is connected via USB the receiver powers up so we have connectivity and power from Pixhawk <==> PPM <==> AR620

Im at wits end as to what to do next. what to try