{
  "jsonrpc": "2.0",
  "method": "public/subscribe",
  "id": 42,
  "params": {
    "channels": [
      "estimated_expiration_price.(index_name)"
    ]
  }
}

{
  "data": {
    "is_estimated": false,
    "price": 3939.73,
    "seconds": 180929
  }
}