Expired Credit: Ensure that your Spirit Airlines credit hasn't expired. Credits typically have an expiration date, and if it has passed, the credit won't be valid for use.

Restrictions and Conditions: Make sure you're meeting all the conditions and restrictions associated with your credit. For example, some credits may only be used for specific types of bookings or within certain time frames.

Booking Eligibility: Confirm that you are trying to use the credit for a booking that is eligible for credit redemption. Not all bookings may be eligible for credit use.

Technical Issues: Sometimes, there might be technical issues with Spirit Airlines' website or booking system. In such cases, it's a good idea to try the process again later or contact their customer support for assistance.

Account Issues: Ensure that you are logged into the correct account associated with the credit. If you have multiple accounts, make sure you are using the right one.

Balance Issues: Check the balance of your credit. If you have used a portion of it before, you might not have enough credit left to cover the full cost of your new booking.

Contact Customer Service: If you've gone through the above steps and your Spirit Airlines credit is still not working, it's advisable to contact spirit airlines customer service number. You provided the customer service number [844-989-7283/1-855-200-0639 (OTA)] in your question. Reach out to them for assistance and clarify the issue you're facing.