Fire state change event websocket API

I’m trying to fire a state change event via the websocket API, but for some reason I can’t make it work.

I can successfully authenticate and receive state changes, so I’m sure my connection to the websocket API is ok.

This is what I’m sending (I’m incrementing the id on every call):

  "id": 2,
  "type": "fire_event",
  "event_type": "state_changed",
  "event_data": {
    "entity_id": "sensor.my_power_sensor",
    "state": 550,
    "attributes": {
      "unit_of_measurement": "W",
      "friendly_name": "Powerful stuff",
      "device_class": "power",
      "state_class": "measurement"

And this is HA’s response:

  "id": 2,
  "type": "result",
  "success": true,
  "result": {
    "context": {
      "id": "01GQG6G6T8Z202RTBWRXWD0MZV",
      "parent_id": null,
      "user_id": "46a99b0006cd4ce6b89c2fbe191125dd"

I can do a similar call via the REST API to change the sensor and that works, but I can’t see any change via the websocket API.

I have tried state_change instead of state_changed but that does not make a difference.