Steam requires specific ports to be open for the Master Server to "see" your host. : Default game port.

Without this tool, your server will remain invisible to anyone browsing by latency, player count, or map name. Players can still join via connect <IP>:<port> , but discoverability drops to near zero.

: Utilities like SteamCMD-AutoUpdate or SteamPS (a PowerShell module) can automate the checking and updating of server files at set intervals.