code: def transaction(self, transaction_id, expand_merchant=False):
          
          endpoint = '/transactions/{}'.format(transaction_id)
  
          data = dict()
          if expand_merchant:
              data['expand[]'] = 'merchant'
  
          response = self._get_response(
              method='get', endpoint=endpoint, params=data,
          )
  
          return MonzoTransaction(data=response.json()['transaction'])
docs: Returns an individual transaction, fetched by its id.
  
          Official docs:
              https://monzo.com/docs/#retrieve-transaction
  
          :param transaction_id: Monzo transaction ID
          :type transaction_id: str
          :param expand_merchant: whether merchant data should be included
          :type expand_merchant: bool
          :returns: Monzo transaction details
          :rtype: MonzoTransaction