Please, do send in a pull request! I really deeply appreciate other people taking the time to look through my code and giving any suggestions they might have.
You should be able to use the build flag “build_flags = -D DEBUGGING_SERIAL_OUTPUT=Serial” but that might give you way, way more than you want to see. There is a LOT of debugging output possible in the library. I’d suggest you open the header (*.h) file for whatever you’re trying to debug and un-comment the define in that header only. The Keller Parent also has a “deep debugging” output which will spit out the raw modbus commands.