Checking your domain name . . . WARNING: Port 443 of computer does not appear to be accessible using hostname: xxx.com WARNING: Connection to http://xxx.com (port 80) also fails.
This suggests that xxx.com resolves to some IP address that does not reach this machine where you are installing discourse.
The first thing to do is confirm that xxx.com resolves to the IP address of this server. You usually do this at the same place you purchased the domain.
If you are sure that the IP address resolves correctly, it could be a firewall issue. A web search for "open ports YOUR CLOUD SERVICE" might help.
This tool is designed only for the most standard installations. If you cannot resolve the issue above, you will need to edit containers/app.yml yourself and then type