When trading on MT4, MT5, WebTrader, or the FXTRADING.com Trading App, you cannot directly modify the lot size of pending orders (such as Buy Limit or Sell Stop). If you placed a 1-lot pending order on gold and later want to change it to 0.5 lots, you must delete the original pending order and place a new one with the updated lot size, price, stop loss, and take profit parameters.
This limitation is not specific to FXTRADING.com—it is a core design restriction by MetaQuotes Software Corp. in the MT4 and MT5 platforms.
Why Can't I Modify Lot Size?
The order modification function (OrderModify) in MT4/MT5 allows you to adjust the price, Stop Loss, Take Profit, and expiration time of pending orders, but it explicitly does not support modifying the trading volume (lot size). This is determined by the platform's API and programming specifications, as confirmed in numerous MQL programming forums and documentation.
If you attempt to modify a pending order in the terminal by right-clicking and selecting "Modify or Delete Order," you'll notice that the lot size field is grayed out or uneditable—only other parameters can be changed.
WebTrader and mobile apps (such as the FXTRADING.com Trading App), if built on MT4/MT5 architecture, inherit this same limitation. No official FXTRADING.com documentation indicates any exceptions that allow lot size modification.
Solution
Manual Method: In the "Terminal" window under the "Trade" tab, right-click the pending order, select "Modify or Delete Order" > "Delete," then place a new order with your desired parameters.
Automated Method: If you use an Expert Advisor (EA) or script, you can write code to first delete the old pending order (OrderDelete), then send a new pending order (OrderSend) while maintaining other parameters.
Important: Ensure your new pending order meets FXTRADING.com's minimum and maximum lot size requirements (typically minimum 0.01 lots, maximum 200 lots), as well as market conditions such as the minimum distance from the current price for pending orders.
This design may be intended to prevent complexity and potential errors during order execution, though it does create inconvenience for traders.