Connect WebSocket API

Establish a WebSocket connection via an HTTP Upgrade request to /ws/v3/trading. The server returns HTTP 101 Switching Protocols when the connection succeeds.

Authentication: pass the JWT access token one of two ways (checked in this order):

• Query string: wss://.../ws/v3/trading?token=<jwt>
• Header: Authorization: Bearer <jwt>

The token must be valid (not expired, not revoked) and the API Key must be granted the tradingws:*:* scope — the trading:*:* scope used by the REST Trading API does not work for this WS connection; it must be granted separately.

Connection limits: at most 10 concurrent connections per API Key; exceeding the limit is rejected with reason Connection limit exceeded.

⚠️ Client implementation note: except when the request is not a valid WebSocket upgrade (a real HTTP 400 returned before connecting), every other rejection reason (401/403/429) happens AFTER the connection has already succeeded (HTTP 101) — the server accepts the connection first, sends a message describing the reason, then closes it. Reason: most WebSocket client libraries cannot reliably surface the HTTP status code of the connection step. Clients should read the first message after connecting to know whether the connection is actually ready to send commands.

Sample rejection message:

{ "code": 401, "msg": "Invalid or expired token" }

Possible rejection reasons: 401 missing/invalid/expired/revoked token, 403 missing tradingws:*:* scope, 429 concurrent-connection limit exceeded, 500 system error.