What is your “ticket” to board Magical Express? Will reservation number work?
Your magic band.
You can use your magic band if you have one. If not (e.g. coming from Canada, pick up MBs at resort), then you receive some vouchers in the mail that you present at Magical Express desk on arrival at MCO. You can also book your Magical Expess ride online or by phone before arriving at MCO airport and they’ll give you a confirmation number for if you don’t receive your voucher in time.
There is also a desk there if you do not have a MB or voucher. They can help you there as well.