Cannot replace world on realm.

I have been trying to start a realm, (which was a lot harder than it should’ve been), and finally started one. But I want to replace that world with a world that I have been working on for a while. I push “replace”, it exports, but after it finishes, it just says “Error: an error has occurred”. I have seen multiple people have this problem, too. Please help.
Version: Bedrock 1.16.50 on IPad