CounterOrderId

public string CounterOrderId { get; }

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using PTLRuntime.NETScript;  

namespace FillsExample
{
     public class FillsExample : NETStrategy
     {
         public override void Init()
         {
             Fills.FillAdded += NewFill;//creates an action that responds to the emergence of a new trade.
         }        

         public override void OnQuote()
         {
             NewOrderRequest request = new NewOrderRequest //creation of a new trading order request.
             {
                 Instrument = Instruments.Current,
                 Account = Accounts.Current,
                 Side = Operation.Buy,
                 Type = OrdersType.Market,
                 Price = Instruments.Current.LastQuote.Ask,
                 Amount = 1,
                 TimeInForce=TimeInForce.GTC,
                 MarketRange = 1000,
             };

             Orders.Send(request); //sends trading order.
         }

         //The method that is triggered after the trade was made.
         public void NewFill(Fill lastFill)
         {
             //outputting of all the information about the trade.
             Print(
                 "--------------------------------------------\n"+
                 "Instrument : \t"    +lastFill.Instrument+"\n"+
                 "Account : \t"        +lastFill.Account+"\n"+
                 "Id : \t"            +lastFill.Id+"\n"+
                 "OrdeId : \t"        +lastFill.OrderId+"\n"+
                 "PositionId : \t"    +lastFill.PositionId+"\n"+
                 "Amount : \t"        +lastFill.Amount+"\n"+
                 "Price : \t"        +lastFill.Price+"\n"+
                 "Commission : \t"    +lastFill.Commission+"\n"+
                 "Profit : \t"        +lastFill.Profit+"\n"+
                 "Time : \t"            +lastFill.Time+"\n"+
                 "Side : \t"            +lastFill.Side+"\n"+
                 "ExternalId : \t"    +lastFill.ExternalId+"\n"+
                 "ExternalPrice : \t"+lastFill.ExternalPrice+"\n"+
                 "Exchange : \t"        +lastFill.Exchange+"\n"+
                 "Type : \t"            +lastFill.Type+"\n"+
                 "Counter Order ID"	   +lastFill.CounterOrderId+"\n"+
                 "--------------------------------------------"
             );
         }

         public override void Complete()
         {
             Fills.FillAdded -= NewFill;
         }
     }
}