Of course, This is logic, that we have to unpack and place there the content of the package. Exactly this I made.

But in the case of the plugin which I wanted to it is RAR.
[url=http://]https://sourceforge.net/p/sweethome3d/p ... Volume.rar[/url]

1) I downloaded the package
2) Unpacked
3) The content I placed into the mentioned directory

look here: