CompleteUrl
This URL will be used by Swedbank Pay when a payment is Completed or Failed.
If your integration subscribes to the onPaymentCompleted and possibly the
onPaymentFailed event, no redirect or use of the completeUrl will take
place. But if you do not have any event handler for the onPaymentCompleted
event, the Swedbank Pay JavaScript will perform an HTTP redirect in the top
frame to the completeUrl. You will still need to do a GET request on the
payment resource to find the final status (Completed or Failed).