Method 1 - From the payments list:
Click on "Payments" in the side menu.
Click on "Create New" in the top right corner.
Enter the amount, date, and payment method, and select a service from the dropdown menu.
Save
Method 2 - From the service detail page:
Click on "Services" on the left side menu.
Select the service to which you want to add the payment.
Click on the Creation payment in the right-hand sidebar menu for payments.
In the payment table, click on "Add".
Insert the amount, date and payment method.
Save.
The associated payment will automatically be associated with the first invoice issued for the service.