Most problems with a Garry's Mod server come down to a few causes. Start with the one that matches what you see.
The panel shows Starting forever, but the game seems to be running
Why: A wrong Steam Game Server Token. The Steam login fails, protection turns off and the server drops out of the list.
Fix: Clear the Steam Game Server Token setting or replace it with a valid token made for Garry's Mod, then restart.
Workshop addons do not load at all
Why: The Workshop Collection setting holds a single addon id, or the collection is private. Only a public or unlisted collection works.
Fix: Make a collection, add the addon to it, set it public or unlisted, and put the collection id in the setting.
Players cannot join after a Garry's Mod update
Why: The server is on an older build than their game, usually because Auto Update is off.
Fix: Turn Auto Update on and restart the server so it updates on start.
The server shows a shortened or odd name in the server browser
Why: The name contains a space, asterisk or question mark, which the game cannot take as part of the name.
Fix: Rename it using only words joined with - or _, then restart.
The server starts on the wrong gamemode or the Workshop gamemode does not appear
Why: The Gamemode setting needs the gamemode's folder name, not the title shown on the Workshop page.
Fix: Enter the lowercase folder name and make sure the gamemode's addon is in your Workshop collection.
Console shows Connection to Steam servers lost (Steam error code 6) and players are dropped
Why: The same Steam Game Server Token is in use on more than one server.
Fix: Give each server its own token.
The server is hard to find in the in-game server list
Why: Servers without a Game Server Login Token are ranked lower in the list, though they still work and are joinable by address.
Fix: Create a token for Garry's Mod with App ID 4000 at the Steam Game Server Accounts page and enter it in Steam Game Server Token.
Still stuck?
Open a ticket in the category that fits and include the last 50 to 100 lines of the console. See How to open a support ticket and How to fix a server that will not start.
