The Frontier Airlines Credit can be used to pay for eligible future flights, services, and fees with Frontier Airlines. To use your credit, enter the required voucher or credit details during the booking process on the Frontier Airlines website or apply it through the airline’s customer service. The credit amount will be deducted from the total cost of your reservation, and any remaining balance may be paid using another accepted payment method. Usage rules, expiration dates, and eligibility depend on the type of credit issued.