PSID不支持的GET请求图API？

Question

我正在尝试在我的fb页面上获取与会话参与者相关的标签。

我的GET请求：<pageID>/conversations?fields=participants,id&access_token=<PageAccessToken>

POST：

    {
      "participants": {
        "data": [
          {
            "name": "Jim Bean",
            "email": "numbers@facebook.com",
            "id": "2821512231253160"
          },
          {
            <my page info>
        ]
      },
      "id": "<convo link>"
    }, 

当我单击参与者的ID时，出现以下错误。

    "message": "Unsupported get request. Object with ID '2821512231253160' does not exist, cannot be loaded due to missing permissions, or does not support this operation. Please read the Graph...",
    "type": "GraphMethodException",
    "code": 100,
    "error_subcode": 33,
    "fbtrace_id": "AwlTn9Vx3mfPtRGnquaHm8k"

因此，我无法请求与PSID相关的标签，而无法获取有关用户PSID的信息。

我想念什么？ 如何从对话中检索PSID？