I have the same issue as the bug report below; every time I try to upload a world to my realm It goes through 100% completion and then gives me a generic error. I see that this has been ongoing for over a month now, and if it can't be rectified soon I would appreciate a refund for the realm I purchased.

https://bugs.mojang.com/browse/REALMS-474?jql=text%20~%20%22cannot%20upload%20world%20to%20realm%22