Welcome to planDisney, Minyoung!
Minyoung, December 31st is such a popular time to visit the Magic Kingdom that reservations for that day are no longer available! If you have not heard of the new reservation system, what you need to know is that you are required to make a Disney Park Pass system reservation to enter the theme park on each day of your visit. This reservation is required for entry in addition to a valid
theme park ticket.
Days like holidays tend to book up pretty quickly, which is why you are seeing that tickets for December 31st are no longer available. Minyoung, since a
Disney Park Pass system reservation is required for entry along with your theme park ticket, you will want to have your tickets purchased and your reservations made before you head out to the parks.
Reservations update in near real-time, so I encourage you to keep checking. You may just luck out and be able to snag someone's last-minute cancellation. If not, I recommend that you plan for another day by checking the handy-dandy
availability calendar.
Sending good luck pixie dust your way!
Sarah B.