Ive been playing on my world with a friend and got annoyed because every time i went offline he had to go too even tho hed like to keep playing. So I purchased a subscription to a 2 player realm and tried to upload our world so that he can play whenever he wants.

When i start the upload Minecraft begins with exporting the levels, thats successful. The next step is initializing upload. Minecraft doesn't show me a loading bar thing for this and brings me back to the 'choose a world to play' screen after about 30 seconds.