When a transaction is authorized the card issuer holds the authorized amount waiting for settlement request to actually process the transaction for payment.
With a Debit card (Credit card vs. Debit card) the authorized amount is blocked directly from the funds on the bank account. Although the amount is not actually processed for payment and it becomes unavailable for use. On online systems of most banks, this authorized transaction will show as "pending" and is easily mistaken by the card holder as a charge.
The amount will be held either until the authorization expires or until the bank releases the amount. Depending on the bank, it can take just 1-2 days to quite a few days.
If the merchant wants to help the card holder get the amount released earlier, merchant may have to contact the issuing bank with the authorization code. Contact details for the issuer can be obtained from the Merchant Service Provider.
See Gift card / pre-paid cards and pre-authorization
