Before making a flight cancellation, there are several points that you need to keep in mind & which are more important:
If you have booked a flight via Allegiant's official website, the first step is to cancel a flight within 24 hrs.
However, you don't need to pay the charges for the cancellation.
Moreover, if you go beyond the time, you must pay the charges depending on the route.
The other essential step related to the Allegiant airlines cancellation policy is cancelling the flight on the boarding date. However, after that, you cannot cancel the trip.
If the traveller gets medically unfit, they can cancel a trip without the cancellation fee.
Apart from these, you'll not get a refund if you have booked a flight via any deals or other ways. However, you can use it for your next trip.