Hi @laughing-gravy ,
Generally speaking, USB Printers can be reached from /dev/usb/lpx. Is that also the case for you? If so, this is already exposed as part of the raw-usb plug.
What I could suggest is that, please run your snap at Ubuntu Desktop first. Probably, you would need to add some additional plugs to your snap. To understand what would be the problem, please run tail -f /var/log/syslog | grep audit in another terminal screen while running your snap to see if there is any permission issue due to missing plugs.
In the meantime, you could try running cups to check if it is possible to print by using your printer.
https://forum.snapcraft.io/t/call-for-testing-openprintings-cups-snap/
Lastly, it could be nice to provide a sample application with a snapcraft.yaml so that people can see and react.