MP Dedicated Server and MP Client connection issues

[Ataros]

Steam can not see your server.
Maybe your provider put you behind a router or your firewall rules do not work (try deleting them and creating again from scratch with everything allowed).

Try creating a server in Multiplayer >> Lobby. Lobby is for those who are put behind a router by provider and do not have real internet IP.

Also try adding your server to Steam >> Servers >> Favorites. It should appear in Game favorites then. Ask someone of your friends to do this too.