Things to check:
- Look at the Intacct.xml for the errored confirmation. Check the key element in the paymentrequestitems list. If that field is blank, make sure the invoice has already been integrated into Intacct. If not, it could be a timing issue. Rerun another Payment Requests batch to try to integrate the invoice, then run another Payment Confirmations batch.
- If the invoice is there, make sure it was not manually paid by someone already. If so, mark the errored confirmation as Integrated.