If I'm not mistaken, they send you a credit voucher/code via email that you use on the Allegiant website when booking your flight.
Can anyone confirm that you do get a code that you can redeem on the web site rather than a code that you have to call (for most, long distance) their 702 help line to redeem?
You do not have to call to redeem actually. There is a box that you type in the code that was emailed to you. Comes up with a message that you have been credited X amount of dollars and your debit card will be billed for the remainder.