About replacing the world

I don't know if it's a specification or a bug, so I'll write it here. sorry...
I accidentally erased the first Realms world by "Download World" in Edit for the world I used in Realms first. Download World
Every time I try to upload the data, I get an error and it is not reflected.
Is it a bug or a specification that the copied world cannot be used?
Please note that the sentence may be strange because I used google translate.