Welcome to the Prismic forum community and thanks for reaching out to us.
This issue is coming because you might be directly compressing a folder, not the ZIP files.
If you have compressed a folder containing JSON files you'd like to import, the import won't work. You need to ZIP the files directly and not a folder.
You need to select all the JSON files and compress them directly. Do not compress the folder they are in. Directly select all the files and compress them.
You can share your repo name with me via a private message so I can have a look.
I have checked with your repository and can reproduce the same error. I have submitted the issue to my dedicated team. I will let you know once I hear back from them.