The customer selects goods in the merchant's shop, and starts the checkout. At this very time:
The customer checks out using Smart Checkout.
Smart Checkout directs the customer to a success URL of the merchant's shop.
When all steps of the process are completed successfully, the Smart Transaction is waiting for a pending payment, or even ready for delivery. It is not guaranteed that the customer opens the offered success URL.
If the customer aborts the checkout, they are directed to the abort URL, if defined. It is not guaranteed that the customer opens the offered URL. They can also simply stop to interact with the browser or close the browser window.