That is a unrelated message
You should enter the path to the html files as zipped up in your zip file
CSS/JS should be linked
<link href="path/to/file.css" />
not
<link href="/path/to/file.css" />
That’s what I mean by relative
Extenion files are uploaded to
https://EXTID.ext-twitch.tv/EXTID/VERSION/ANOTHERSTRING/
Hence the need to use relative URLs to CSS/JS