Plugin will not install Error 404

Site Origin Page Builder. I have just come across this and it looked so good I thought I would try it, but after several attempts and downloaded twice, the plugin refuses to unpack. I cannot seem to find any contact details for the plugin owners and the only forum I am directed to is WP. For a supposedly industry leader plugin, it is a miserable failure from my perspective. Does anyone know the answer as it really looks good. But is that all…It look good, its a good idea, but it does not work.