Is there a way to 're-import' an invoice?

If you are using QuickBooks, you can delete the invoice from QuickBooks and the system will ask if you want to re-import the next time you sync. 

Unfortunately, there is no way to do this from Sage. If you are using Sage or do not want to delete the invoice from QuickBooks, you will have to void the invoice in your accounting software and create a new invoice in ServiceBox. When you void an invoice in your accounting software, the connector will ask you if you want to void it in ServiceBox too the next time you sync.