Ah, yeah, sorry, buildNumber was the field. It seems like this issue on the website is problem with a lot of games so it might be something with their uploader and not your game because a lot of the other games I've tried to upload via the site have given me this error. Here is the error message on their site just in case it helps you at all
EDIT: looking at the SDK docs, it is a bit misleading since it seems to state that you can leave out that value but the website seems to think that you can't, haha!