想知道用REST API执行监听的参数

Question

我打算指定执行Firestore监听API https://firebase.google.com/docs/reference/rest/firestore/v1beta1/projects.databases/listen的最小参数，但响应为400无效。

我的要求缺少什么？

POST https://firestore.googleapis.com/v1beta1/projects/metal-tile-dev1/databases/(default)/documents:listen

{
 "addTarget": {
  "once": false,
  "query": {
   "structuredQuery": {
    "from": [
     {
      "collectionId": "cities"
     }
    ]
   }
  },
  "readTime": "2017-09-06T03:32:02.951319Z"
 }
}

https://developers.google.com/apis-explorer/#search/firestore/firestore/v1beta1/firestore.projects.databases.documents.listen?database=projects%252Fmetal-tile-dev1%252Fdatabases%252F(default)&_h=8&resource=%257B%250A++%2522addTarget%2522%253A+%250A++%257B%250A++++%2522once%2522%253A+false%252C%250A++++%2522query%2522%253A+%250A++++%257B%250A++++++%2522structuredQuery%2522%253A+%250A++++++%257B%250A++++++++%2522from%2522%253A+%250A++++++++%255B%250A++++++++++%257B%250A++++++++++++%2522collectionId%2522%253A+%2522cities%2522%250A++++++++++%257D%250A++++++++%255D%250A++++++%257D%250A++++%257D%252C%250A++++%2522readTime%2522%253A+%25222017-09-06T03%253A32%253A02.951319Z%2522%250A++%257D%250A%257D&