Hi Hervé,
the download key is set (J3) in the plugin /. extension or in the key manager (J4). The key is then passed to the joomla updater.
Every plugin / extension has its own download url, so setting up a generic one that does all will not work.
I have no experience with yoursites so I have no clue as to if they use the joomla updater (like mysites.guru does or if they have their own logic (like watchful.li).
the download links for e.g. ochFitvids is:
Code:
https://onlinecommunityhub.nl/index.php?option=com_ochsubscriptions&view=updater&format=xml&element=ochfitvids&key=[12345...67890]
btw, I use ubuntu and FF and copying the download key works fine. can you see if you get an error in the browser console when clicking the button?