Does a user require special permission to work with the scan and pay plugin?

Does a user require special permission to work with the scan and pay plugin?

No. To be able to use the Scan and Order plugin features you do not require any special permission or priviledge. If you have access to the Web Register, you are good. You can always navigate to Home > Setup > User Management > Roles to check the permissions assigned to your role. 

Plugins in Tagrain are either Subscription Based or License Based. So the price that you pay for your plugins is based on the number of POS terminals that you have in your setup and the number of licences that you have acquired.
There will be no change in your subscription amount in the current billing cycle if you are only deactivating the Scan and Order plugin AND not updating your Store / POS count.