I'm not sure about the exact meaning of your question. I don't think that this issue is CBSubs-side but more that it is Paypal side. CBSubs uses Paypal Website Payments Standard and that has no methods to specify or restrict any payment methods of paypal.

Isn't there any link on your paypal payment page with "No paypal account?" as text ?

Do you have a screenshot of the payment page ?

Did you try with (another) browser with all cookies erased ?

Once you used Paypal with a browser using a paypal account, Paypal sets a cookie to that browser, to avoid using directly a credit-card with paypal. But browsers without paypal account still see the credit card form possibility. This is "documented" on Paypal forums.

Also, in Paypal settings, check "My Account" / "Profile" / "My selling Tools" / "Block payments: Limit payments, add instructions, and more." that it does not block credit cards which are not on file.

If all of the above fails, and even accessing from another computer with different IP address and first of all all cookies erased fails, please contact Paypal's support to understand why even no link displays for credit-cards. In all cases, please let us know what the issue was.