User Roles - Sales

I have granted the user access role of Sales to a new user of our MYOB and as Read-only.  However when the user opens the Sales Register and clicks on an invoice to view it the History button is available but when clicked on a message comes up saying they don't have access to this function (or something like that).  How do I fix this as we need the user to be able to see what credits/payments have been applied to an invoice?