1. Confirm which backend you launched
Iron Gate says -crossplay uses the PlayFab crossplay backend. Without that argument, the server uses the Steam backend and only Steam users can see and join it. This is the first branch in the troubleshooting path.
2. Steam backend: check ports 2456–2457
The official dedicated-server guide says the Steam backend requires a port range with Internet access. The default server port is 2456 and Valheim also uses the specified port + 1, so the default range is 2456–2457. Router port-forwarding must match the configured server port.
3. Check whether you intentionally hid the server
-public 1 is the default and makes the server visible in the browser. -public 0 hides it and makes it joinable through the Join IP flow instead. A hidden server is not necessarily a broken server.
4. Crossplay backend: do not troubleshoot it like Steam
Iron Gate says crossplay uses a relay and does not require router port forwarding. It can be joined with the public route, server list or Join Code, but not through a local IP or loopback address.
5. Verify the server actually reached the connected state
The official setup guide says the dedicated-server console should report Game server connected when it is ready to accept connections. If the process never reaches that state, fix the launch/configuration error before debugging client discovery.
6. Mixed platforms: check versions before network surgery
Valheim 1.0 hotfixes can reach platforms at slightly different times. If one platform suddenly cannot join while others can, verify compatible client/server versions before changing the world, deleting saves or rebuilding the server.
Official references
Iron Gate dedicated-server guide · Crossplay FAQ
Unofficial guide. Product and game names belong to their respective owners. Always check current official patch notes before changing a server or important save.