The merchant submits an authorization request via their payment processor. This request is passed on to the acquirer who forwards the request to the card issuer. The card issuer verifies that sufficient funds are available to cover the cost of the transaction and returns the result to the payment processor. The payment processor in turn returns the result to the merchant. The authorization is either approved with an authorization code, or declined with an error code indicating the reason.
If the transaction is authorized, the funds needed to cover the transaction are put on hold until the transaction is completed. If authorization fails, an error code is returned instead and the transaction cannot be completed.
Authorization may fail because the payment information is incorrect (e.g. the credit card number is wrong or the CVV does not match the card number), because the buyer has insufficient credit to cover the cost of the transaction, or for technical reasons. If the issue is caused by incorrect data, the buyer can correct the data and the authorization request can be resubmitted.
This process only takes a few seconds.