What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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Was there any specific error why some users could not fill in the CC details on the form?
I just made a test using your jotform http://www.jotform.us/form/50395136326151
but so far I could not reproduced the problem. I could fill in the billing information on the CC of the Paypal payment tool just fine
Please let us know if the issue persist.