Top reasons for card declines include incorrect CVC (the 3 digit code on the back of your card or the 4 digit code on the front of your American Express card), expired card, or insufficient funds. Quickly check to see if you have entered the CVC correctly and whether your card is expired.
Declines may also be caused by the fraud protection that is applied automatically by your bank or financial institution.
Your bank or card issuer can provide a more detailed explanation about why your card may have been declined. Reach out to them directly to see what they suggest.