For Confluence Server users the first thing our add-in will ask you for is the Confluence Base URL.
Confluence Server is hosted by your company, so they can basically give it any URL.
If you are unsure about the Confluence Base URL, the most reliable way is to just copy the homepage URL from the Confluence overview:
Due to technical limitations, the Confluence system must have the corresponding app installed, and it has to be available from the internet. If this isn't the case, a connection to Confluence is not possible.
For further details please check the Detailed Technical Requirements.