The installation script try to run the Service Discovery procedure for your almost-installed server and it seems that your server has a problem with that. The SD procedure is very important, because thanks to it other servers know the precise address (API endpoint) where they should send messages to your server’s users.
To fix the SD procedure settings, you should check location and contents of the
privmx-configuration.json file. It should be placed in the main folder of your web page or in
privmx subfolder. It should contain a valid URL set as the API endpoint. Check also your domain’s DNS entry (if you have entered privmx configuration entry there).