> oxide.grant group default cupboardmessage.use
Permission 'cupboardmessage.use' doesn't exist

Ofcourse its doesn't exist because plugin description is wrong ;)
permission is: cupboardmessages.use

it says in the overview cupboardmessages.use
https://umod.org/plugins/cupboard-messages

It was fixed already.

When I looked at it yes but not when he did so was pointing that out as I did not know it was updated