“Steamworks is not initialized” or EventSystem errors when pressing Play #

Press Play in the bootstrap scene, never in the menu or session scene. Those scenes have no camera or event system of their own, so starting them alone produces EventSystem errors and Steam calls before Steam is initialized. From 6.1.19 the menu logs a clear warning if it is started on its own, and SteamLobbyGameObjectEnabler and SteamLobbyChatUI no longer throw when Steam is missing. Also check that Steam is running and signed in, and that the App ID is accepted (the Ready badge in the Steamworks project settings).

A valid player is not accepted after a rejected one #

Fixed in the Toolkit: a stale auth session was left behind when BeginSession returned anything other than OK, so a later valid answer for the same user went to the wrong callback. The Toolkit now registers a session only when Steam returns OK. If you wrote your own handling, check the return value and call EndSession on failure. See the Steam authentication article.

Friend List showed the local user #

Fixed in the Toolkit sample: the Friend List could list the local player. Update to the latest sample.

Leave button seemed to do two things #

Fixed in the sample: the menu Leave button had two duplicate Leave calls in its On Click list in all six samples. Keep a single SteamLobbyLeave.Leave entry when wiring your own.

“Setup needed” box appears as soon as you press Play #

Added 2026-10-02 (uncommitted in the samples). Allow Listen Server is off for the App ID, so the host could not start a Steam Game Server. Click Open Steamworks settings (Editor only), tick Allow Listen Server, generate the code, and press Play again. Dismiss hides the box for the session. The check re-runs every frame, so the box clears once fixed, and the same text is logged. Related: “The Steam Game Server did not come online” on Start Session has the same cause, or Steam is not running.

Quick Match or a public lobby fills with strangers #

App ID 480 (Spacewar) is shared by every developer, so those lobbies are everyone’s. Join by lobby ID, or use your own App ID, for a private test. The Play popup now shows an amber note saying this.

Start Session keeps failing after editing scripts in Play Mode #

Older setups could leave a Steam Game Server running natively after a recompile in Play Mode. Current Foundation shuts it down before a reload. If it still happens, restart the Editor.