Why wasn't my order executed at the declared price?
This may happen to Buy Stop, Sell Stop, and Stop Loss orders.
When these orders are triggered, the system sends the Market order that is executed at the current price, which may differ from the declared price.
Other types of pending orders (Buy Limit, Sell Limit, and Take Profit) are mostly executed at the specified price; and sometimes at the better price, if this exists on the market at the time of execution.