Go to the
Configuration menu > → System Values: Basic > → Payment Plans.
Click the Add button on top of the Payment Plans table. You will be directed to the Add Payment Plan page.
In the Name field, provide a name for the new plan.
Decide whether this plan should be Active and thus selectable.
Decide whether this plan should be marked as a Preferred Item and thus appear on top of the drop-down lists.
Decide whether this plan should be a Default one.
Click the Save button.