My original request may not have been clear, so apologies for that, but the payment that the refund is for is not linked to an invoice - it's an overpayment.

So, Day 1:

100 in payments from payment gateway but there's only a 50 invoice. Customer has overpaid by 50.

Day 2:

Customer wants refund of 50. Create expense for 50

Day 3:

150 in payments is received from payment gateway, but this is because it contains 200 debit and 50 credit for the refund. 200 still needs to be linked to a new invoice (different customer). The -50 needs to be applied to the refund expense. So the bank recon is only 150. A new invoice is 200. And the refund (expense) is -50.

Hope that explains it a bit better.