S2 doesn't currently ship with a credit card validator.
It is, however, trivial to write your own server-side validators.
On the client side it's not as straight-forward until I get the hack in to allow user-written client-side validators, although they won't be configured like the default built-in ones are; you'll just register them with the existing client-side validation code per-page.
I hope to get it in before the S2.1.3 release, but may not have the time. I'll also provide a patch and documentation so it can be used with existing versions.
Currently I have been working on one Auction Project and this project have facility to transfer online balance, deposit money to PayPal Account so i want to validate credit card.
But in one thing I need you favor I have integrate PayPal SDK for transfer money and deposit money to user's account but in local it transfer once and now it gives internal error So, can you please tell me why PayPal transaction done only once. And now gives us to internal error.Help me ASAP.