In the invoice table (tab "Invoicing" ① > Menu "Invoices" ②) there is a column "UnPayed". In this column, the outstanding amount shows in red or if the invoice is payed the word "payed" in green.

If you click the amount ③ , a popup will appear ④ where you can give in the payment for the invoice by clicking on new ⑤ (Invoices can also partially be paid, eg an advance.).

You will get a new popup where you can enter the amount, the date, the name of the party and a comment. After the entry, click on the Save icon to save the transaction. The pop-up will then close, and the transaction summary adjusts.