Hi,
Was payment received for the product initially and is now needing to be refunded due to item lost/undelivered?
If yes, you’ll need to record the payment as being received against the invoice, and then issue a credit note and refund amount to clear it; this article will help you do that: https://help.crunch.co.uk/s/article/how-to-refund-a-client2
If no payment was received for the product at all?
Do not add a payment to the invoice otherwise it’ll create a refund and cause complications. Instead, simply raise a full credit note against the invoice; this article will also help - scroll down to the bottom and follow the heading “Raising a full credit note”: https://help.crunch.co.uk/s/article/how-to-raise-a-customer-credit-note-before-an-invoice-is-paid2
We hope this helps and feel free to get in touch if you have any other questions - Alexandra