A payment can be declined by number of reasons. The most common are:
- Insufficient funds;
- Invalid card details;
- Your card has expired;
- Your billing address does not match the address on your card statement;
- CVV/CVV2 number is incorrect or incomplete.
You have to make sure that you give all details correctly. If you can't yourself resolve this unpleasant issue and payment still get declined, you should contact your card issueing bank to specify the decline reason. If bank unblocked the card and payment still get declined then it's better to contact support team of the site or use another payment method.