There is an API for payment processing of credit cards. You can find it here
I will try to provide you with a sample code.
We have plans to implement "Points based Shopping Cart" as one of our features for future versions of Sitefinity eCommerce.
However the current version of Sitefinity has limited capabilities in extending the eCommerce system
Adding custom payment methods is not supported in this release. However it is in something we are looking into for the next release of Sitefinity.
the Telerik team
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