Are you sure you are importing the right json? I mean not some palette json or something like that? Could you send me the file so I could check it? Or maybe just paste it here if it's small enough?
I thought I was doing it right- here's the file. https://drive.google.com/file/d/1-LS-mMnuAqgBuXCz6BQk8bXt8gZgItq8/view?usp=shari...