错误：即使是可选的参加者，findMeetingTimes也会抛出“ AttendeesUnavailable”

Question

我正在尝试使用MSDN Outlook Calendar website上记录的https://outlook.office.com/api/v2.0/me/findmeetingtimes端点。当我使用以下负载调用端点时：

 {  
  "Attendees": [  
    {  
      "Type": "optional",   
      "EmailAddress": {  
        "Name": "Studio 3", 
        "Address": "PDXICSTUDIO3@rogueInc.onmicrosoft.com"  
      }  
    }  
  ],   

  "TimeConstraint": {  
    "ActivityDomain":"Unrestricted", 
    "Timeslots": [  
      {  
        "Start": {  
          "DateTime": "2018-10-30T19:30:00",   
          "TimeZone": "UTC"  
        },   
        "End": {  
          "DateTime": "2018-10-30T20:30:00",   
          "TimeZone": "UTC"  
        }  
      }  
    ] 
  },   
  "ReturnSuggestionReasons": "true", 
  "IsOrganizerOptional": false, 
  "MaxCandidates": 99 
  } 

我收到一个空的会议时间建议响应，原因为“ AttendeesUnavailable”。我将与会者的类型声明为attendeeBase Resource Type documentation中指定的“可选”，“必需”还是“资源”似乎都没有关系。这似乎是GraphAPI的错误，我不确定如何继续。