Whether you are using a SmartShop handset or the SmartShop app on your mobile phone, you can pay at a dedicated card-only SmartShop checkout or at a self-checkout that is SmartShop enabled (varies between stores).
If you are smart shopping in a convenience store using the SmartShop app on an iPhone, you may be able to pay with Apple Pay and avoid the checkouts completely (available in selected stores, see store signs).