Click To be paid Invoices info-card on the invoice page and you will find all the invoices which have to be paid.
Select the Invoice, scroll the page down, fill out the Payment Date and the Sum to pay, then click Pay to mark a payment.
To mark several Invoices as paid, click the Payments button on the Invoices page.
Create Payments--> select a supplier for a new payment.
Fill in the requested fields--> create one payment for the selected documents-->click Pay.