{
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      "replyToken": "REPLYTOKEN12345",
      "source": {
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        "type": "group"
      },
      "timestamp": 1553506027708,
      "mode": "active",
      "joined": {
        "members": [
          {
            "userId": "U111111",
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    }
  ],
  "destination": "Uab012345678901234567890123456789"
}