The e-Payment Paypal is a payment processing facility to allow the users of the e-Payment plugin to use their Paypal account or any Paypal method of payment offered to be used to pay an invoice online.
The Paypal extension integrates seemlessly, although once installed, you must enter the login and password codes before your clients can run payments with this process. This is done in the e-Payment / e-Payment Paypal settings.
The system also offers a test mode so one can make sure the system works before using the full fledge real version of the system. In the sandbox mode, you should always be able to process payments even if your source accounts says it is empty. This is allowed as if you had an infinite source of money on those user accounts.
IMPORTANT NOTE: Also it happens rather rarely, we have had problems with the Paypal sandbox, which at times gives us the wrong URI to futher process payments. We do not have a choice but to use the wrong URI and thus the payment fails in such circumstances. The once we have seen were 127.0.0.1 (localhost, yes). When that has happened in generally did last for a day or two and then things come back to normal.