How to cancel unpaid balance from AP Invoice

Hello Gurus, We have payables on Oracle EBS R12.1.3. We have an old invoice that was partially paid (using prepayments for employee) and there is still some balance left on invoice.Business users confirmed they don't want to pay the remaining balance ( 6 year old invoice). What's the recommended process to clear / cancel balance amount on this invoice ? Invoice is Validated and accounted (and partially paid). Inputs highly appreciated.