Plex on a zyxel nas326?

https://www.file-extensions.org/article/show-and-hide-file-extensions-in-windows-10

When you have disabled the hiding of 'known file types', you should see the .txt or .doc extension of web_prefix, and you can remove it. The file shouldn't have an extension.

Well, I don't know what to say. The package manager looks for a file admin/zy-pkgs/web_prefix. If it exists, it will use the content as, well, a webprefix to exchange ftp://ftp2.zyxel.com/ . It will not check if there are files which have a similar name, or an extension.

If Windows Explorer says web_prefix is a text document, it probably has an extension, as AFAIK Explorer doesn't look into the file, only at it's extension. So you have to strip the extension, which you can't do if you can't see it. Open notepad, create a new file, and save it. As long as you can't see it's .txt extension, you have to fiddle with Explorer's settings until you can see it. And then look at web_prefix again.

Apparently you succeeded in installing MetaRepository. Next step is updating the package list in the firmware package manager, and installing the 'Plex installer' package.