Salesforce users receive error when trying to use QBOE button

Forums: 
I h ave a number of SF users who need to use Dbsync to create invoices from opportunities. I have set up the DBsync login credentials on their user profiles, but when they use the Update Opportunity to QBOE button, they receive a permissions error. If I give them system administration rights, they are able to use Dbsync. But I don't want them to be system administrators, obviously. Do I need to create a permission set for Dbsync? Or is there something else I have missed in the setup?