The redirect URLs are used to navigate the customers back to the partner page when they complete the checkout process. The redirect URL must be specified in Create Order API parameters.
When the customer completes the checkout page the customer will be redirected to return_url_on_success.
If there are any issues completing the order then they will be redirected to return_url_on_failure.
If the customer cancels the flow at any point, they will be redirected to the return_url_on_cancelled.