Most problems with an ARK: Survival Evolved server come down to a few causes. Start with the one that matches what you see.
Players cannot find the server in the in-game list
Why: The list is slow to refresh and ARK only shows a server once it has fully started; the name must also match what you set.
Fix: Wait until the badge says Online, refresh the list, and search for your exact Server Name. Make sure the list is set to show unofficial servers.
Epic Games players cannot join
Why: Epic players only get in when the server runs with crossplay enabled, and ARK's docs say two options are needed together, not just one.
Fix: Put -crossplay -PublicIPForEpic=<your server IP> into Extra Launch Options, then restart. If the Server Address on the Overview page shows a name instead of numbers, ask support for the server's IP address. If Epic players still cannot join, contact support.
Admin commands do nothing in the console
Why: You must authenticate first with the server's admin password, and on multiplayer servers commands need a prefix.
Fix: In game, press Tab, type EnableCheats and your Admin Password, then use cheat or admincheat in front of each command. In the panel Console, type the command without any prefix. The password uses only letters, numbers, dashes and underscores.
Players are told the server is on a different version, or cannot connect after an ARK patch
Why: Client and server versions must match, and the server only fetches a new game build at start when auto-update is on.
Fix: Turn on Auto-update server in Settings, then Game Settings, and restart the server.
The server takes a very long time to start after adding mods
Why: The server downloads and installs every Workshop mod on the first start after the list changes.
Fix: Let it finish and do not restart it midway. Later starts are faster. If it still never comes up, remove the newest mod IDs and restart.
A mod map does not load, or you see The Island instead
Why: Adding a mod that provides a map does not switch the map by itself.
Fix: Set Server Map to the exact map name the mod provides and restart.
Edits to GameUserSettings.ini or Game.ini disappear
Why: ARK rewrites its ini files on shutdown, so edits made while the server is running are lost.
Fix: Stop the server first, edit the file in the Files tab, then start the server.
A mod will not work or players on an older client are refused
Why: Some mods and older clients do not work with BattlEye.
Fix: Turn BattlEye Anti-Cheat off in your settings and restart; be aware the server then has no cheat protection.
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.
