UCS activation issues when using a webbrowser

This article contains information and solutions about errors that can occur when activating UCS via webbrowsers.

What happens when UCS is activated via a webbrowser?
Javascript running in the browser makes a https request to our license server (https://license.univention.de) with the email address entered by the user and the currently installed UCS core edition license.
The server will then generate an activated license for the UCS system based on the LDAP base and send it to the provided email address.

Error 0: An unknown error occured. Please try it again later!
This error was observed with browser privacy addons such as Privacy Badger. The addon blocks the request to https://license.univention.de.
To resolve this issue, allow the connection to the website.
Depending on the addon, one has to allow the connection, allow the request for the activation website or put the UCS server on a whitelist

It should then be retried to request the license