Receiving a different price on your trade that you have requested is known as slippage. This can either be positive and negative and is due to the fast-moving nature of the instrument that you were trading. When an order is triggered, it is sent to the market to be filled, and this will be completed at the best price available in the market at that time. Markets were closed can also cause slippage as the market may open at a different price from where it closed.