10000 — send_not_open

Client-side: sendJson ran while the socket was not open. This is not a Worker close, and it is not terminal.

At a glance — no HTTP status · SDK FluxySendError.

What to do

• Call attach() / connect() first, and wait for connected before sending.
• Gate sends on the connection status (attaching → attached) — see Connection status.
• The SDK's guard message spells this out: "Cannot send: WebSocket is not open. Call connect() and wait until connected."

Related

• 50000 connection_failed