Refund and adjustment credit notes are automatically generated, just like invoices. However, you can manually create an adjustment credit note for an invoice in the Payment Due status.
Go to the unpaid invoice card by clicking on it and select Create credit note from the list of options in the top right corner of the page.
In the window that appears, the purpose of the credit note has already been selected. Since the invoice is only payable, the note can only be an adjustment note.
Next, specify the amount by which the invoice is to be corrected.
Finally, select the reason for the adjustment.
Click the Proceed button to complete the transaction.
