I have a small app that connects to the REST API backend server where it gets data such as phone number and text and then sends SMS messages. It works like a charm. On the other hand, I developed the same thing on the Raspberry Pi3 with a GSM/GPRS modem but as a stand-alone SMS gateway that has its own rest API server integrated.
I know there can be all kinds of servers on Android as it is based on Linux, so the most obvious question is why there is no extension for a simple REST API server with JSON and JWT? Anyone here that would bite into that and develop it?