If you have problems making payments with your credit card, please make sure you have enough funds and your billing details (like CVV code) are entered correctly. If you prefer to pay in local currency, you can do it using Visa and Mastercard only. You must choose USD in payment page if using a different card. However, if you still have any issues, please review the URL where you get an error and contact the company through which you're doing the payment. For example, if you're making payment through BitPay, please contact BitPay :)
Alternatively, if you get an error on PayPal side when you are trying to pay with PayPal, please contact PayPal support team, they will gladly assist you.