Stuck on Notification API WebSocket subscription handshake

Stuck on establishing the Notification API WebSocket connection for real-time event ingestion. My gRPC service attempts to upgrade via wss://api.mypurecloud.com/api/v2/analytics/events but receives a 1006 abnormal closure immediately after the initial Sec-WebSocket-Accept response. I am passing a valid OAuth Bearer token in the Authorization header, yet the server drops the connection before I can send the subscription payload.

  1. Verified token validity via /api/v2/authorizations/userinfo.
  2. Confirmed endpoint matches the documentation for event streaming.

Any insights on why the handshake fails at this stage? Thanks.