delay in profit loss

You can refer to this similar thread.

The whole point is to defer polling the positions. Now you want to calculate the same P&L with the last price provided in the same response.

You need to use GetQuote or websocket to get the latest last traded price. The last price in the positions response is a cached value.

public void getmtm()
        {
            kite = new Kite(MyAPIKey, Debug: true);
            initSession();
            kite.SetAccessToken(MyAccessToken);

            PositionResponse positions = kite.GetPositions();
            //pnl = (sellValue - buyValue) + (netQuantity * lastPrice * multiplier);
            decimal pnls = 0;
            for (int i = 0; i < positions.Net.Count; i++)
            {
                Dictionary<string, Quote> ohlcs = kite.GetQuote(InstrumentId: new string[] { positions.Net[i].InstrumentToken.ToString() });
                decimal LastPrice = 0;
                foreach (KeyValuePair<string, Quote> entry in ohlcs)
                {
                    LastPrice = entry.Value.LastPrice;
                }

                pnls += (positions.Net[i].SellValue - positions.Net[i].BuyValue) +
                (positions.Net[i].Quantity * LastPrice * positions.Net[i].Multiplier);
            }
//get pnl in label
          lbl_mtm.Text = pnls.ToString();
            

        }

Learn Algo Trading

https://youtube.com/watch?v=wFih_6X5nV8&t=11s