When swiping your CoinZoom Visa Debit Card at many locations the merchant requests authorization for a specified fiat amount. If you were to purchase a five dollar cup of coffee, for example, they would request five dollars. If you had enough value in your crypto wallets CoinZoom would authorize that purchase and initiate a market order for the amount of crypto to satisfy the payment maid.
Some merchants aren't sure how much you're final purchase will be, so they request a "pre-authorization" for a dollar amount. For example, gas pump transaction may request a "pre-authorization" for $80.00. After you finish pumping your gas they would send a "completion transaction" message with the actual amount to charge.
Example of merchants where this can happen include gas stations, hotels and rental car agencies.
CoinZoom will release any pre-authorized amount from your account once the merchant notifies with the "completion transaction" amount and the actual amount to charge.