There is a limit for the file size of 500mb. Please let us know the application IDs of the source (3.x) and the target (4.0) apps so we can copy it for you.
I did however encounter a 401 issue right after. I then realized the migration brought over the old app’s iOS App Key (I had already started development on the 4.0 app before migrating). After updating the key, everything’s running fine again, just thought you should know.