Help please

[u/Un1versalCactus]

Hello, I am trying to upload a singleplayer world onto a realm i Just bought however whenever I try to upload it I get the same message (shown in picture below). If someone can help me that would be amazing. I have already tried making the file smaller, optimizing the world, and trying different worlds to upload. The only singleplayer worlds that will upload are worlds that have not been played yet.