Why was my order cancelled with "Pending order was cancelled by the exchange at the end of the trading session"?

Your order was cancelled because unmatched pending orders are automatically cancelled when the market closes. The exchange cancels all unmatched orders that haven't been executed by the end of the trading session.

The validity of your unmatched order extends until the market closes. All unmatched orders are cancelled at the following times in their respective segments:

If the exchange doesn't match your order (meaning it's not executed), you need to place your order again for the next trading session. You can use AMO to place orders beyond market hours or GTT if you want the order to stay active for 365 days.