Hello there, Karolina.
Let me show you how to add a credit note to a paid invoice.
Let's open the payment transaction so we can link the credit note. You can follow these steps:
You can also refer to this screenshot and article for more details: Enter and apply credit notes.
Please post again if you need more assistance with this. Have a great day!
I'm happy to know that the steps provided by my colleague AlexV about applying credit notes to invoices work perfectly on your end. Just in case you have any other QuickBooks questions in the future, feel free to get back to us here on the Community page. We're always here to help.
Also, skim through our help articles if you need tips and related links while working with QuickBooks in the future.
Have a wonderful day ahead!