Purchase payment means paying the supplier for the Purchases.
In the add purchase screen, you can add the payment for the purchase.
In list purchase click the actions for any PO and it will display the list of actions for it. This option is not displayed if there is no payment due.
Go to contact -> Suppliers. Click on actions for the supplier and it will show “Pay Due amount”, click on it and pay the amount. The “Pay Due amount” option is not displayed if there is no payment due.
Follow the Add/Edit Pay-Via / payment method.