Subscribe to a single event with websocket api

Configuration Frontend
1

My question is simple…
I successful subscribe to events from a webpage with long token with (summarized) this code:

                socket.send(JSON.stringify({
                    "id": 3,
                    "type": "subscribe_events",
                    "event_type": "state_changed"
                }));

Now, if i wish to subscribe to a specific event:

socket.send(JSON.stringify({
    "id": 3,
    "type": "subscribe_events",
    "event_type": "state_changed",
    "event_filter": {
        "entity_id": "sensor.beb_consumo_istantaneo_condominio"
    }
}));

it fails.
I can filter entity id with first code, but wish to reduce lan traffic…