If you have a credit/debit card payment declined and you have enough money in your account to cover the payment, there are a few conditions that can prevent your payment from going through:
-The payment amount exceeds your daily spending limit.
-Your card has been locked by your issuing Bank. This often happens when you enter incorrect information or PIN code more than a few times.
-Your browser connection is extremely slow and it's not allowing your transaction to go through.
The solution to the above problems is to contact your Bank and ask them to unlock your card, if the problem continues you can avoid this issue by making sure you're using a fast connection while placing your transaction.