This reservation credit/electronic voucher is easily usable by entering the credit code at checkout. Can be used under ANY NAME and can be used for multiple bookings until the full value is used. The amount can also be used to pay for fares, bags, seats, vacation packages, fees, and taxes on Spirit.com. Redeemable for trips booked by December 31, 2021 on ANY flight available in the system.
Here are direct instructions on how to book your next trip using Spirit Airlines Reservation Credit: https://customersupport.spirit.com/en-us/category/article/KA-01232