The server is running, but it does not appear on the list! | Sven Co-op | Page 1

I'm not professional when it comes debugging server issues but do please check if your ports are forwarded and firewall configured.
Although, if you are creating a server just for your friends, perhaps this will be a better solution rather than making a dedicated server:
https://steamcommunity.com/sharedfiles/filedetails/?id=1705149010

Steam Community :: Guide :: Creating a game for your friends withou...

Learn more about how to create a private game for your friends quickly and easily. This requires no port forwarding, no special router configuration, no firewall rules, and no other networking

#The server is running, but it does not appear on the list!