Originally posted by noodle:

Hm... I was able to properly upload a zip file using Windows' compressed zip file. What OS are you using?

Windows 10.

Originally posted by noodle:

That could mean the zip file is corrupt. How did you create the file?

I simply created a ZIP file on my desktop.

Also, I managed to upload the mod on the site as a 7z file.

I'm trying to upload an updated version of my mod "The Binding of Torchic" and it's saying that it's not a ZIP file when it is! I'm using Mozilla Firefox, too.