Your card purchase may get declined due to several reasons:
Some banks may decline online transactions when noticing an unusual frequency of them. You should contact your bank and clarify the status of your online payments, as well as mention the site you are trying to pay;
Your 3D Secure system is not activated, and you should check with your bank;
You should check the availability of your funds;
The card’s expiration date or CVV should also be verified. Please make sure that you are filling in the correct card details;
Due to the excessive amount of bank-declined attempts, you might have been blocked by our velocity check. You can try again to add funds in 10 - 15 minutes;
Your attempt might be blocked due to an IP conflict. You can add funds without using a VPN or changing your normal IP address.
A solution for all the situations above would be to try another card issued by a bank.