If you are using the Linux / macOS version of Lady Heather the com port selection rules are a bit different. You specify a com port number 1 greater than the operating system device number. This horrible kludge is due to the fact that Linux starts numbering com ports from 0 and Windows starts at 1. /0 is used to disable the com port. Or for Linux and macOS you can use /id=device_name to specify the device name. Also for Linux / macOS and you are using a USB connected serial device / cable you need to put a "u" after the device number. "/1u" (or "-1u", command line options can start with either "/" or "-") specifies device "/dev/ttyUSB0", etc. macOS uses "/dev/tty.usbserial#" as the device name