code: def get_refund_transaction(self):
          
          try:
              url = self._refund_transaction_url
          except AttributeError:
              raise ValueError("No refund transaction is available for this transaction")
  
          resp, elem = self.element_for_url(url)
          value = self.value_for_element(elem)
          return value
docs: Retrieve the refund transaction for this transaction, immediately
          after refunding.
  
          After calling `refund()` to refund a transaction, call this method to
          retrieve the new transaction representing the refund.