Banks try to protect clients' assets as much as possible, so their risk control often makes normal payments fail. If you fail to pay by credit card, just try a few more times and it will work. And You can also pay with PayPal.
If you do not have a PayPal account, please select PayPal still at the checkout page & click the complete order button. Then you'll be directed to a page with access to both PayPal and Debit/Credit card payment (for the latter option, you don't have to register for PayPal).