Can I cancel my Allegiant flight without penalty? Yes, Allegiant airlines offers a 24-hour risk free cancellation policy 1-844-949-8748 . You can cancel any flight within 24 hours of booking for a full refund without any fees 1-844-949-8748 as long as your departure date is at least seven days away.
Source: https://bcpportal.bcpcouncil.gov.uk/forums/general-discussion/5bfc051a-d39d-ef11-95f5-6045bd11e914