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Right now the invoice number is just a text field however, a lot of merchants like the idea of using the express app but think that this functionality could really help tie everything together.
Scenario:
If an invoice/order number is entered that does not match then it will work just as it does today where it is just a record for the merchant to refer back to and will show on the payment grid.
If an invoice/order number is entered that does match, the payment will be associated with that invoice/order.
If the merchant overcharges on the QP or Express app when doing so it is okay, we do not restrict this on the web either, we will leave it up to the merchant to accept the responsibility that if it was a mistake that they issue a refund for the proper amount now that we allow a merchant to do partial returns via Express and Payment Detail.