回复8楼:美国的航空公司都允许购票后，24小时之内免费取消，不管便宜票还是全价票。

Thanks to a federal rule established by the U.S. Department of Transportation, you can cancel your flight to, from, or within the U.S. within 24 hours of when you booked it for a full refund. It doesn't matter which airline you're flying or where you're coming from or heading from, as long as the flight touches U.S. soil, you have up to 24 hours to cancel it for free and get your money back – not just a voucher or travel credit.
https://thriftytraveler.com/guides/24-hour-rule-free-cancellation/