When you need to refund part of a payment on account, follow these steps.
EXAMPLE: You have a £100 payment on account and you want to refund £80, leaving £20 as a payment on account.
Go to the original payment on account record. Edit it to reflect the new amount you wish to retain. For example, change a £100 payment on account to £80.
For the remaining amount, create a new payment on account. In this case, record another payment on account for £20, dated the same as the original payment.
Now, process the refund of £80. This refund will correspond to the adjusted amount in the payment on account.