code: def exchange_to_margin(self, symbol, currency, amount, _async=False):
          
          params = {'symbol': symbol, 'currency': currency, 'amount': amount}
  
          path = '/v1/dw/transfer-in/margin'
          return api_key_post(params, path, _async=_async)
docs: 现货账户划入至借贷账户
          :param amount:
          :param currency:
          :param symbol:
          :return: