Allegiant Airlines missed flight policy is strict—if you don’t check in or arrive before the cutoff, you may lose your entire fare. Cancellations within seven days of departure are non-refundable unless you purchased Trip Flex, which allows a one-time change or cancellation up to one hour before departure. Without Trip Flex, missed flights are treated as no-shows, and no credit is issued. Always check in early to avoid losing your ticket. Need help with Allegiant...