When your credit card is declined, the only information we receive from your bank is that the payment didn't go through.
These are possible reasons your card is being declined:
Incorrect card number or CVV/CVC
Make sure your credit card information is up-to-date. Read Where can I update my billing information? to learn how to update your information.
If you've double checked your credit card information to make sure it's correct, your best bet is to get in touch with your bank to ask that the payment be accepted.