If you want to manually register a supplier invoice as paid, go to Supplier Invoices – Supplier Invoice. Select the invoice you want to mark as paid from the list:

You will now see the invoice details. Click Register Payment:

In the window that appears, you can modify the payment date, payment method, paid amount, and enter any deviations (e.g., reminder fees). In the Add Deviation Account field, select the correct account. Press Enter to add a new row if needed.

Once all the information is correct, click Register Payment. The payment will now be marked as paid.