code: def handle_get_txn_req(self, request: Request, frm: str):
          
          ledger_id = request.operation.get(f.LEDGER_ID.nm, DOMAIN_LEDGER_ID)
          if ledger_id not in self.ledger_to_req_handler:
              self.send_nack_to_client((request.identifier, request.reqId),
                                       'Invalid ledger id {}'.format(ledger_id),
                                       frm)
              return
  
          seq_no = request.operation.get(DATA)
          self.send_ack_to_client((request.identifier, request.reqId), frm)
          ledger = self.getLedger(ledger_id)
  
          try:
              txn = self.getReplyFromLedger(ledger, seq_no)
          except KeyError:
              txn = None
  
          if txn is None:
              logger.debug(
                  "{} can not handle GET_TXN request: ledger doesn't "
                  "have txn with seqNo={}".format(self, str(seq_no)))
  
          result = {
              f.IDENTIFIER.nm: request.identifier,
              f.REQ_ID.nm: request.reqId,
              TXN_TYPE: request.operation[TXN_TYPE],
              DATA: None
          }
  
          if txn:
              result[DATA] = txn.result
              result[f.SEQ_NO.nm] = get_seq_no(txn.result)
  
          self.transmitToClient(Reply(result), frm)
docs: Handle GET_TXN request