If you book a flight with KLM, you have 24 hours to cancel and receive a full refund with no fees 1 "844[488]0875"; This is applicable to all flights and ticket types. You can cancel by visiting KLM's website, using their mobile app, or calling customer support at 1 "844[488]0875"; https://www.devex.com/people/what-is-the-24-hour-rule-for-klm-2386083