Sometimes it is possible that there is an error on the invoice you have already created, and your customer will ask you to send them a new corrected invoice. You can't just delete an invoice, but you can correct the error by issuing a credit note.
The invoice cannot be deleted, as invoices must have sequential numbering. This is determined by the Accounting Act.
You can make a credit note by navigating to "incomes" in the UKKO system, opening the invoice by clicking the correct invoice or the three dots shown next to the amount of the invoice. You'll then find the "issue credit note" option in the menu.
Please note that before issuing a credit note, the payment entry on the invoice must be deleted! The entry will be removed by clicking the trash can icon next to the payment information in the transaction preview. So first click the invoice. After that you will see the information regarding the invoice. Scroll down until you find the "Payment events" section. There you will see the payments towards this invoice. Next to the amount is the trash bin.
If the original invoice has been sent as an e-invoice, e-mail invoice, or letter, the refund invoice will also be sent by the same method.