My card was declined but there is nothing wrong with my card.
This type of problem is often caused by using a credit/debit card from a country other than the USA to pay for a product/service being sold from the USA. Credit card companies often prevent these kinds of transactions due to suspected fraud. From their perspective, if you always use your credit/debit card to buy products in your country and suddenly, you buy something from the USA, they flag this behavior as unusual. They may prevent this specific charge or they may block your card completely. Usually a phone call to your credit/debit card company or bank will fix this. You simply tell them that you are buying something in the USA and to approve your card for the purchase. This fixes the problem in 90% of cases. Another common problem is mistyping your credit/debit card number, expiry date or CCV code. Be very careful to type correctly the digits from your card into the online form.