I bought tickets through expedia a couple of year's ago for our trip last year. I ended following advice on a thread at the time about this and just tracked it down...
"After buying the tickets (6 in my case) I setup everyone on My Disney Experience, but of course the voucher codes Expedia sends through aren't recognised.
I waited 3 days to allow time for Expedia to inform Disney that tickets have been purchased before giving My Disney Experience Technical and Website Support a call on 0800 16 90 749.
They took my MDE email, voucher numbers and Expedia itinerary number and passed the details on to their backoffice team. I was told it could take a few days before I heard anything, but within an hour I'd received an email confirmation, and the tickets were associated in MDE. Good to go!"
If I remember correctly I rang disney about a week after ordering with Expedia. Explained I had purchased a UK ticket via expedia and what numbers I needed from them so I could link on my MDE. They were super helpful, put me through to the right team and they found the numbers for me.
Also, just to add.. if you have old magic bands, if they are still live and active on your account, once your tickets are linked, you don't even need to collect your physical ticket with the voucher... once on mde, just go to the gate on go on through! worked fine
