You have to use your customized link to register for the promotion or you will get the error about the promotion already being over. Search for an email from Frontier Airlines ([email protected]) on 2/29 with the subject "ONE DAY ONLY: Leap into $29 flights for the 29th". That will contain your personalized link which will allow you to register. The link might be single use only so make sure you have your Frontier Miles number ready to go when you click on it. I also found it difficult to get the registration form to submit so good luck!