Operating system: Mac OS X
Slicer version: 4.6 and 4.7
Expected behaviour: downloadable
Actual behavior: non-downloadable extensions
Probably you are behind a firewall that blocks the Extension Manager. Try to manually download and install the extension using your web browser, as described here: https://www.slicer.org/wiki/Documentation/Nightly/SlicerApplication/ExtensionsManager#How_to_manually_download_an_extension_package.3F
Thank you for the help. I was able to download the extensions now.