Microsoft Graph findMeetingTimes endpoint not work

Please do not report as duplicate because all other topics have not solved my issue, thanks.

I'm using Microsoft Graph api to list and create calendar events, however I can't seem to make the findMeetingTimes endpoint work.

This is my authorization URL:

https://login.microsoftonline.com/consumers/oauth2/v2.0/authorize?client_id=xxxxx&response_type=code&redirect_uri=xxxxx&response_mode=form_post&scope=openid%20profile%20User.ReadWrite%20User.ReadBasic.All%20Sites.ReadWrite.All%20Contacts.ReadWrite%20People.Read%20Notes.ReadWrite.All%20Tasks.ReadWrite%20Mail.ReadWrite%20Files.ReadWrite.All%20Calendars.ReadWrite&state=12345

Then I request an access token using the same scopes:

$request = json_decode($guzzle->post('https://login.microsoftonline.com/common/oauth2/v2.0/token', [
            'headers' => [
                'Content-Type' => 'application/x-www-form-urlencoded'
            ],
            'form_params' => [
                'client_id' => 'xxxxx',
                'scope' => 'openid profile User.ReadWrite User.ReadBasic.All Sites.ReadWrite.All Contacts.ReadWrite People.Read Notes.ReadWrite.All Tasks.ReadWrite Mail.ReadWrite Files.ReadWrite.All Calendars.ReadWrite',
                'code' => $auth_code,
                'grant_type' => 'authorization_code',
                'redirect_uri' => 'xxxxx',
                'client_secret' => 'xxxxx'
            ],
        ])->getBody()->getContents());

After that I'm trying the findMeetingTimes endpoint using:

$request = json_decode($guzzle->post('https://graph.microsoft.com/v1.0/me/findMeetingTimes', [
            'headers' => [
                'Authorization' => 'Bearer ' . $accessToken,
                'Content-Type' => 'application/json',
            ],
            'body' => '{
              "attendees": [
                {
                  "type": "required",
                  "emailAddress": {
                    "name": "My Name",
                    "address": "myemail@hotmail.com"
                  }
                }
              ],
              "timeConstraint": {
                "activityDomain":"work",
                "timeslots": [
                  {
                    "start": {
                      "dateTime": "2019-04-02T09:00:00",
                      "timeZone": "Pacific Standard Time"
                    },
                    "end": {
                      "dateTime": "2019-04-03T17:00:00",
                      "timeZone": "Pacific Standard Time"
                    }
                  }
                ]
              }
            }',
        ])->getBody()->getContents());

However, it keeps returning:

401 - Unauthorized: Access is denied due to invalid credentials.

You do not have permission to view this directory or page using the credentials that you supplied.

Who's going to be my hero? :/

This is by design. From the documentation: