test.gs

config = {
  'team': 'xxx', //チームID
  'token': 'xoxb-xxx', //トークン
  'headers':{
    'authorization': 'Bearer ' + this.token,
    'Content-Type': 'application/x-www-form-urlencoded',
  }
};
  
method = {
  //ワークスペースのユーザ一覧を取得
  workSpaceUserList: function(){
    var url = 'https://slack.com/api/users.list';
    
    var options = {
      "method" : "post",
      "payload" : '',
      "headers" : config.headers,
    };
    
    var res = this.apiRequest(url, options);
    Logger.log(res);
    return res;
  },
  
  //招待メール送信
  invite: function(){
    var url = 'https://slack.com/api/admin.users.invite';
    
    var data = {
      'email': "xxx",
      'channel_ids': "xxx",
      'team_id': "xxx",
      'token': config.token,
      'set_active': true
    }

    var options = {
      "method" : "post",
      "payload" : data,
      "headers" : config.headers,
    };
    
    var res = this.apiRequest(url,options);
    Logger.log(res);
  },
  
  //招待するユーザのフィルタ（botを除外する）
  inviteUserFilter: function(){
    
  },
  
  apiRequest: function(url, options){
    return UrlFetchApp.fetch(url, options);
  }
}

function myFunction() {
  method.invite();
}