It is not possible to add a new payment method as a reseller. There is a menu Add New Payment System:
Home > Configuration Director > E-Commerce Settings > Payment Systems > Add New Payment System
but the button "Save" is missing.
The reseller is not expected to have possibility to add new payment systems, as stated in the reseller guide: "PBA is delivered with a pre-configured set of payment systems, processing centers, and associations. You can not add or remove payment systems or processing centers, you can change associations or create own."
The menu "Add New Payment System" availability for the reseller has been reported as #PBA-44798.