If you wish to make a payment for one of your customers, here are the different steps to follow:
Click on the "Customers" menu, then go to the desired customer profile
Click on "New payment".
Then select the transaction(s) you would like to pay by ticking the different boxes
The amount is automatically adjusted according to the transactions chosen. (You can change the price if you wish)
Then choose the "Payment Method".
The incoming payment date is based on today's date, you can select another one
Click on "Validate"