Notification API WebSocket drops on /v2/notifications/conversations/events subscription

Connection holds fine during handshake, but dies immediately after subscribing to conversations.events. The server sends a close frame with code 1000.

DEBUG: Sending sub request: {"id": "req-1", "type": "subscribe", "data": {"topic": "/v2/notifications/conversations/events", "filters": {"query": "state!=closed"}}}
DEBUG: Received close: {"code": 1000, "reason": "Normal Closure"}

Tried removing the filter, same result. Token is valid for other REST calls. Is the topic path wrong or is there a rate limit on sub requests?

might be the filter syntax. docs say query needs specific format. try:

var sub = new SubscriptionRequest { 
 Topic = "conversations.events", 
 Filters = new NotificationFilter { Query = "state:open" } 
};

standard != often breaks the parser in .NET SDK. check the NotificationFilter class definition.