Usually its the confirmation # . Its been about 2 years but the 8 digit code from Orbitz did link in my MDE.
Disney will not help with it however ME will.
If you can't get any of those to work wait a few days then call Magical Express to book. When they enter your info they can see the disney conf # , so just ask for it if needed.
Hopefully you won't need to do that. Should work now.
It will be the confirmation #. However, if not working, you will need to contact Orbitz to get the right number. I had to do this a few months back but it was no big deal; was a quick phone call and they got the # to me right away.