It is very important that when you encounter a duplicate invoice, you follow the below steps for verifying if it is actually a duplicate or not and follow appropriate steps depending on which circumstance it is.

If you notice a duplicate symbol on the list of invoices you are processing, or the duplicate bar on the invoice in the details view, you need to make sure you take action and not process an invoice that is a duplicate of another in the system.

If you click on the duplicate symbol, or the duplicate bar, a search tab will open and it will show you all the invoices that are in the system with the same invoice number and vendor as the one you've clicked on. There will be at least two invoices, but there could be more than that if you have more than two invoices with the same vendor and invoice number.

Double click on the row for the first invoice, or click on the view details icon to get into the details view of the first invoice. You will want to open the first invoice, and then using the previous and next buttons, navigate to the second invoice to compare the invoice images.

If the invoices ARE duplicates of each other, then you will delete the invoice(s) that are the earliest in the workflow (in the example above we would delete the IP invoice not the invoice in A status). 

If the invoice IS NOT a duplicate of the others, then you need to edit the duplicates so they have unique invoice numbers. If the invoice is still editable, you simply need to change the invoice number and submit for approval, but if the invoice is in PA, A, EX or SE, you must reset the invoice, change the invoice number and resubmit for approval.