code: def transfer(self, sub_uid, currency, amount, transfer_type, _async=False):
          
          params = {}
          path = '/v1/subuser/transfer'
          params['sub-uid'] = sub_uid
          params['currency'] = currency
          params['amount'] = amount
          params['type'] = transfer_type
  
          return api_key_post(params, path, _async=_async)
docs: 母账户执行子账户划转
          :param sub_uid: 子账户id
          :param currency: 币种
          :param amount: 划转金额
          :param transfer_type: 划转类型，master-transfer-in（子账户划转给母账户虚拟币）/ master-transfer-out （母账户划转给子账户虚拟币）/master-point-transfer-in （子账户划转给母账户点卡）/master-point-transfer-out（母账户划转给子账户点卡）
          :param _async: 是否异步执行
          :return: