Please ask your client following:

Please contact your credit card issuer/bank at their 24/7 phone number and ask them for the reason they are not authorizing your payment to www.joomlapolis.com .

They will be able to tell you and normally to fix the issue within minutes, so that you can just re-try. Sometimes they block international payments until you call, but they can block for a variety of reasons. They can tell you the reason for sure.

Alternatively, you can pay through Paypal and 2Checkout as backup methods with a credit card without creating accounts there.