Answer: look up your router model and follow the guide on this site.
GameRanger - Launching Game Problem
Description: When trying to connect to a game lobby, you receive a warning "Firewall Problem - You appear to have a firewall or router that is blocking you from playing games."
Fix: The is because your router/firewall is blocking the necessary ports required to access the server (UDP/16000), either forward these ports to your PC (if you know how) or try using a VPN to work around the issue if you do not have access.
GameRanger - Hosting Problem
Description: You are able to join game sessions, but cannot host any of your own even though the port forwarding in your router is set up correctly.
Fix: Try deactivating compatibility mode in Windows 10 by right-clicking 'The Moon Project.exe' and unchecking the appropriate section in the application properties. There is a high chance GameRanger is unable to set up the virtualized TCP environment, because it gets confused about what operating system the game is running on.
GameRanger - Unable to enter game lobby
Description: When the game lobby starts, the green dot briefly appears and disappears while you likely receive one of a number of errors reported back.
Fix: This is likely because your version of the game is run as admin, to fix this also ensure GameRanger is run as admin.