01 Capture the symptom first
Copy the exact client error and timestamp. Record whether all players fail or only one, and whether the problem began after an update. Confirm matching client and server versions before changing network rules. Redact IP addresses and secrets before sharing logs publicly.
02 Confirm the application is listening
A running process is not proof that the world loaded successfully. Read the startup log for a ready state and check the configured listen address, port and transport protocol. Use the game’s current documentation; query ports and gameplay ports may be different.
03 Move out one boundary at a time
Test locally, then from the LAN, then externally. If LAN works and external access fails, inspect inbound firewall rules, router forwarding and whether you have a publicly reachable address. Do not disable the entire firewall as a permanent fix. Change one rule, test, and record the result.
04 Know when to ask the provider
If you cannot control the network edge, send support the game build, configured ports, sanitized startup errors and the results of each boundary test. Never include an admin password. This evidence is more useful than repeatedly reinstalling a working server.