American Airlines Cancellation Policy or United Cancellation Policy: United And American Airlines is no exception to the 24-hour flexible booking policy. You may cancel or change any flight within 24 hours without incurring additional costs.
Air Canada Cancellation Policy: you have up to 24 hours after booking to cancel your ticket for any reason and receive a full refund with no change or cancellation fees.
Southwest Airlines Fees - Southwest Airlines flight change policy is simple: no change fees if you need to modify your flight reservation
https://aviationrepublic.com/american-airlines-cancellation-policy-how-to-cancel-flight-booking-with-aa/
https://aviationrepublic.com/blog/how-to-cancel-united-airlines-flight-ticket/
https://aviationrepublic.com/blog/air-Canada-cancellation-policy-how-to-cancel-an-air-canada-flight-booking/
https://aviationrepublic.com/blog/southwest-airlines-flight-change-cancellation-and-other-fees-all-you-need-to-know/