This is posted on the InDesign forum Overview page: "
Latest Update: We are aware of issues with installing Add Ons for InDesign CC 2015. If you require Add Ons to work with InDesign, we encourage you to use the previous version until we have a fix in place."
Thank you for bringing that to my attention.
For future reference, where should my downloaded and installed templates appear and how do I use them?
how did you verify, that your extension is indeed installed?
I downloaded the addon which automatically installs it. To check, I then downloaded it manually and used the extension manager.
It asked me to overwrite the conflict which was the previously installed version.
Just Correcting here. We have now resolved the problem. You can download the latest update of the Creative Cloud desktop app from: Download Adobe Creative Cloud apps | Free Adobe CC trial. Run the installer, it is a force update will fix the extensions not visible in the InDesign app issue. After the installation of creative cloud desktop app, relaunch your app, Now your extensions started syncing. and they will start reflecting at the required location.