*Stock trading, countries: UK only.
Your order was executed at a different price than when it was placed because the stock prices fluctuate throughout the day. Price volatility is one of the stock market properties. You will be able to see this price fluctuation as you place the order during market hours.
You could also place an order outside of market hours and your order will be pending until the market hours open. When the market hours open, your order will be executed immediately at the available price. Note that this price might be different from the price that was available when you initially placed your order.