I have had this problem in the past, you need to have a serial number set. I made a custom board for an arduino mega so I could run 6 on one board. I had to set the serial number of each board using the support library.
https://kegbot.org/docs/kegboard/support-library/
set-kegboard-serialnumber
It isn’t in the kegbot server checkout, it is in the kegboard checkout.