Setting spi_port seems to be what is killing the initialization of my RFM69 so will see what that actually does.
int SIGFOXClass::begin()
{
#ifdef SIGFOX_SPI
spi_port = SIGFOX_SPI;
reset_pin = SIGFOX_RES_PIN;
poweron_pin = SIGFOX_PWRON_PIN;
interrupt_pin = SIGFOX_EVENT_PIN;
chip_select_pin = SIGFOX_SS_PIN;
led_pin = LED_BUILTIN;
#else
// begin() can only be used on boards with embedded Sigfox module
if (_configured == false) {
return false;
}
#endif
Edit: decided to use software SPI for the RFM69 in the end, still interested to know why this doesn't work.