There are several reasons why a credit/debit card may be declined. You may have exceeded the daily transaction limit or the available credit/debit amount on the card.

Alternatively, there might be an error with the card number, expiration date, or CVV code. Please ensure that these details are correct. Also, verify that the card is valid and not expired.

Finally, contact the card issuer to confirm that the card is approved for online transactions and that no protective measures are preventing the transaction.