Adding an Interest Payment to a Sales Invoice
Go to Sales → Invoices
Click the eye icon on the invoice row to open its details
In the Description field, select Interest
Enter the interest amount, e.g., 1.50 euros
Click the plus (+) button to save the payment
2. Removing an Unmatched Reference Payment (when bank connection is enabled)
Go to Sales → Payments
Filter by Only unmatched payments
Click the trash bin icon on the row of the reference payment to delete it