A build check error in the area "manifest.json". An error: the game cannot be published until it is fixed.
The build check runs on every game LobbyLab builds, and each problem it finds has a stable code, the exact message, the file and line when it names one, and a link to this page.
What the check looks at
manifest.json describes the game: its slug, title, player counts, execution profile, join policy, subscriptions, smoke intents and settings. It is strict JSON with no unknown keys.
How to fix it
Write strict JSON: double quotes, no comments, no trailing commas.
Fix the field the message names. Player counts are 1 to 16, subscriptions includes member.join_requested and session.start_requested, and every smoke intent's actorIndex is below minimumPlayers.
See also: every error code, the API reference and the docs.