How can I send post request with json data on flask-dance?

I'm trying to send POST request to google calendar's free-busy service on my flask dance extension. But I'm getting "405 Method Not Allowed" error. I don't know how to debug it.

I have to pass JSON data in the request body. I have referred request documentation . I'm new to flask and flask dance any help would be appreciated.

@app.route("/",methods=['POST'])
def free():
    if not google.authorized:
        return redirect(url_for("google.login"))
    event = json.dumps({"timeMin": "2019-03-31T00:00:00Z",
             "timeMax": "2019-04-01T00:00:00Z",
             "timeZone": " Asia/Calcutta",
             "groupExpansionMax": 3,
             "calendarExpansionMax": 1,
             "items": [
                 {
                     "id": "abcd@gmail.com"
                 }
             ]
            })
    resp = google.post(url="https://www.googleapis.com/calendar/v3/freeBusy",data=event)
    return resp.json()

response should be json data

  "timeMax": "2019-04-01T00:00:00.000Z", 
  "kind": "calendar#freeBusy", 
  "calendars": {
    "abcd@gmail.com": {
      "busy": [
        {
          "start": "2019-03-31T03:00:00Z", 
          "end": "2019-03-31T09:00:00Z"
        }
      ]
    }
  }, 
  "timeMin": "2019-03-31T00:00:00.000Z"
}```

Added GET with POST, now code seems to work

@app.route("/",methods=['GET','POST'])
def free():
    if not google.authorized:
        return redirect(url_for("google.login"))
    event = {"timeMin": "2019-03-31T00:00:00Z",
             "timeMax": "2019-04-01T00:00:00Z",
             "timeZone": " Asia/Calcutta",
             "groupExpansionMax": 3,
             "calendarExpansionMax": 1,
             "items": [
                 {
                     "id": "abcd@gmail.com"
                 }
             ]
            }