@marc the Atom should arrive soon, we want to test out the board with the Helium Client so that we can hit the ground running once we receive the kit.
#if defined(ARDUINO_AVR_UNO) || defined(ESP8266) seems do have done the trick, thanks. Replaced both Helium.h and Helium.cpp .
As to why SoftwareSerial and not Serial1,
Serial1 uses UART1, TX pin is GPIO2. UART1 can not be used to receive data because normally it’s RX pin is occupied for flash chip connection.
Since this is a simulation, maybe it would be best to give full feedback once we are setup, it should be any day now.