https://www.devex.com/people/understanding-full-process-is-it-worth-it-to-upgrade-to-delta-premium-select-2059526

https://**********runtheedge.com/threads/1-86o-544-0078-what-is-united-airlines-24-hours-cancellation-policy.4042/

https://**********runtheedge.com/threads/united-faqs-take-full-guide-for-united-airlines-cancellation-policy.3555/

https://**********runtheedge.com/threads/q-a-can-i-cancel-a-flight-and-get-a-refund-in-qatar.3424/