Occasionally, your issuing bank might decline a transaction because of “Insufficient Funds”. After checking your account, you discover that there are funds available for the purchase.
This can happen if there are other transactions in your account for which there is temporary authorisation. An authorisation can block the amount of the transaction in your account, thus reducing the available balance.
Time-wise, the authorisation has limited duration. After is has expired, the balance will be restored to your account.