Hello, larkinar.
They can take a picture on the invoice then uploaded it in the computer so they can attach it on your vendor’s bill. For additional information about attachments in QuickBooks Online, please refer to this article: https://quickbooks.intuit.com/community/Getting-Started/Attachments-in-QuickBooks-Online/m-p/185993.
Please consider posting here again if there’s anything else you need with QuickBooks.