POST /updates/pv HTTP/1.1
Host: alto.example.com
Accept: text/event-stream
Content-Type: application/alto-updatestreamparams+json
Content-Length: 120

{
  "add": {
    "ecspvsub1": {
      "resource-id": "endpoint-cost-pv",
      "input": <ecs-input>
    }
  }
}