To create a payment for an open customer invoice directly, you can click on Register Payment at the top of the form.
From there, please select the payment method (bank, cash, etc…) and the amount you received from the customer. By default, KIU will propose the entire remaining balance on the invoice for payment.
You can also register a payment to a customer directly without applying it to a customer invoice. To do that, go to Accounting-> Customers-> Payments. Then, from the customer invoice you will be able to reconcile this payment directly.