You can reverse allocations of credits against already paid bills. Please see the steps below on how to action:
From the DPS home screen, click Client Postings.
From the drop-down, click Ledger Card.
Enter Matter Ref and click Search.
Locate the credit that paid the bill, this could be an OCR/CTO/NTO transaction type. once located, double-click on the credit.
Click on the Payment Against tab.
There should be a row showing the allocation against the bill. Hover your mouse over the row and right-click, then click Reverse Allocation.
Once the allocation is removed the bill will become unpaid and can either have a credit applied to it or it can be reversed.