Spirit Airlines doesn't charge a single penny for a seat while check-in however you have to pay for your desired seat. In the free seat assignment, you get randomly assigned seats at check-in, and in this way, you may or may not sit with your friends and family. But you can purchase a seat by paying a seat selection fee. The Spirit Airlines seat selection fees start from $5 and may vary depending on several factors like routes, location of the seat in the aircraft.
Besides, if you don't know the procedure to select a seat prior to the flight check-in, you can go through the information mentioned in this post. Above all, to make it easy and simple for you here is a list of steps for you to follow.
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