使用谷歌脚本中的RTM API将子（回复）消息发送到松弛通道中的线程时遇到问题

Question

我创建了一个链接到电子表格的Google脚本，该电子表格用于在更新单元格时向松弛通道线程发送消息。消息正好发布到频道，但是我无法获得'thread_ts'属性来将消息作为对父消息的时间戳指示的特定线程的回复发布。我已多次阅读文档。我做错了什么？

function myonEdit(e) {

    var sheet = SpreadsheetApp.getActiveSheet()  
    var range = e.range;
    var columnOfCellEdited = range.getColumn();

    if (columnOfCellEdited == 7) {
        var url = "https://hooks.slack.com/services/xxxx/xxxx/xxxx" ;
        var currentRow = sheet.getActiveCell().getRow()
        var name = sheet.getSheetValues(currentRow, 1, 1, 1);

        var payload = {
            "username" : "robot", 
            "text" : name,
            "icon_emoji": ":robot_face:",
            "icon_url" : "http://image",
            "thread_ts": "1511829070.000023"
       }

    sendToSlack_(url,payload) 
  }
}

   function sendToSlack_(url,payload) {
   var options =  {
       "method" : "post",
       "contentType" : "application/json",
       "payload" : JSON.stringify(payload),
  };
  return  UrlFetchApp.fetch(url, options)
  }