@_dpdp_ for some reason a cookie is not getting written in your browser's cache when you click on the button.
If you use the Sketchucation ExtensionStore tool as Rich shows, it will install extensions directly so you don't have to download them to your computer and then use Install Extension in the Extension Manager. In addition to making extensions easier to install the first time, using the Sketchucation ExtensionStore to install extensions from here means when extensions get updated you can find out and quickly update them. In addition you can see what extensions you've installed and when you move to a new computer or a new version of SketchUp, you'll have a bundle of extensions that can be installed automatically. The Sketchucation ExtensionStore is required for license management for paid extensions like those from Fredo6, too.