If you miss the delivery the courier will usually re-attempt the next working day or will leave a card, instructions on how to arrange another delivery will be noted on the card.
Please check your tracking to see if your item is out for delivery as you will get 2 delivery attempts.
You can also arrange to collect the items from a local depot.
For same-day deliveries within Belfast (Captain Courier), you will only get one delivery attempt and then the item will be returned to sender. This will incur a failed delivery fee and no refund will be offered.