Know more about Spirit Airlines Infant Policy
Spirit Airlines allows infants under two years to fly for free on an adult's lap on domestic flights. If you prefer, you can purchase a seat for the infant at the standard fare, provided you bring an FAA-approved car seat. International travel requires a ticket for infants. You must present proof of age, such as a birth certificate. Strollers and car seats can be checked at the gate for no additional charge. For a more comfortable flight, consider bringing toys, snacks, and other essentials to keep your infant entertained and comfortable during the journey. Source: https://medium.com/@henryjose759/what-are-the-rules-for-infants-on-spirit-airlines-5622d7ef2cc5