in case someone is running through the same problem, this is the answer I received from the support staff:
[quote:33eo8rfl]Dear CAFOFO,
There is indeed a limit on the package's size you can upload.
Please try to split up this package in 200 MB max packages. You can provide them as "versions" of the same item your users will be able to download at once.
Let us know if you encounter further issues uploading your item to the store.
Kind regards,
Julien
Scirra Ltd