sendFederatedCallStart was sending `https://${domain}/livekit` as the LiveKit URL. The LiveKit SDK requires `wss://` for WebSocket connections. The caller (local) worked because it gets the URL from config.livekit.url (wss://). The federated acceptor failed because it used the relay URL (https://) — the SDK can't connect over HTTPS. Now uses config.livekit.url directly, falling back to wss:// if unset.