Webhook URL is your store's URL through which Stripe informs your store about any changes in the order. For example, if you refund a payment transaction for a certain amount via Stripe backend, Stripe will send information about this refund to the store using a special request to the Webhook URL, and the store will update the order status to refunded. If Webhook URL is not specified, the store will not know that the order was updated in Stripe backend and the order status in the store will not be updated automatically.