After redirect back to merchant, the payment is still in PROCESSING status.

In some rare cases it may happen the payment is not in final status at the moment of redirection back to merchant but still in PROCESSING status (i.e. the bank has not processed the payment yet).

Merchant should inform the customer the payment is still being processed and that the customer will be notified once the payment is processed successfully (via email, in the customer’s e-shop account etc.). The merchant needs to implement background process of payment status checking (polling payment detail endpoint in some intervals, or, once available, use web hooks).

Customer interrupts the payment process and does not return to merchant’s e-shop page.

These situations can be handled by webhooks functionality. Alternatively this can be treated by polling the payment detail endpoint by the client in some interval. However this is much worse approach comparing to webhooks.