A. Unfortunately, Southwest vouchers require that you complete travel before the expiration date. You can sometimes get an extension of up to six months, however. Contact customer service to see if you qualify. Other airlines, such as Frontier, allow you to book your flight during the voucher’s validity period and fly anytime you can book a fare. Some United vouchers require flying during the validity period, others allow you to book during the validity period and fly later. These rules are subject to change and vary from airline to airline.

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