Hi @Daniel_Rohde,
can you please describe what are you trying to achieve?
Which one of this 2 use cases match your setup?
- you have an FrSky tx/rx combo like an Horus + an X8R,X4R or R9
- you’re using a long range system such as DragonLink, ULRS or TBS or perhaps EZWifibroadcast
I understand that you have OpenTX 2.2.3, good, that is a requirement.
I read you have ardupilot but which version?
Option 1
Ardupilot sends telemetry packets down the radio link in native frsky format, for this to work
- flash your flightcontroller with a recent ardupilot firmware
- enable frsky passthrough telemetry on one of your serial ports by setting SERIALn_PROTOCOL = 10 where n is the number of your serial port, you do this with mission planner by going to full parameters or with QGroundControl in the telemetry setup page.
- get yourself an inverting cable such as this one
Option 2
Ardupilot produces mavlink messages and these need to be converted to frsky telemetry either in the air or on the ground. The most common use case is on the ground where a teensy converts mavlink messages to frsky telemetry packets and feeds them into the Horus which displays them with the Yaapu Widget
For this to work you need
- get a board supported by Eric’s firmware (Teensy, etc)
- configure and compile the firmware for your board and use case (air/ground/relay)
- wire according to the docs
enjoy your new system 
Alex