maybe a level problem ? the Rx/Tx lines should be 3V3
this a my (unsorted) browserfolder 811 dump 
- https://create.arduino.cc/projecthub/naresh-krish/integrate-node-red-with-rak811-lora-node-using-the-ttn-c4564a
- https://github.com/RAKWireless/RAK811-AT-Command/tree/master/Application%20Notes
- https://github.com/RAKWireless/RAK811-AT-Command/blob/master/Arduino/RAK811/RAK811.h
- https://github.com/RAKWireless/RAK811-AT-Command/tree/master/Arduino/RAK811/examples
- RAK811 Lora Module Connecting to TTN
- https://github.com/RAKWireless/RAK811-AT-Command/blob/master/Software%20Development/RAK811 LoRa AT Command V1.3.pdf
- https://github.com/RAKWireless/RAK811-AT-Command
- https://www.hackster.io/naresh-krish/using-the-rak811-lora-module-with-arduino-a38de8
- https://create.arduino.cc/projecthub/naresh-krish/getting-started-with-the-rak811-lora-node-67f157
- https://www.hackster.io/naresh-krish/using-the-rak-811-lora-node-with-android-things-13f7df