1. Placed downloaded realm from friend in saves folder
2. checked so it works on single player
3. minecraft realms
4. configure realm
5. reset world
6. upload world
7. choose my map
8. wait for upload to finish
9. see attachment

I have looked around on other posts with this exact issue, and can't really come up with a solution.

Realm name is Pahchi_Survival

Edit: I also sometimes get upload failed (-1)

Edit2: I created a completely new world and tried to upload that as well, which resulted in the same error. Starting to think that the problem lies at mojang.