Order notifications are used to notify customers or Billing administrator about sales orders' status changes (order place, renewal order confirmed, renewal charge failed, order canceled). Usually, they are sent by order flow transition, for instance, when fraud screening check fails, when services provisioning completes successfully, when credit card charge fails or succeeds. Order notification can also be sent by an event handler. The most important event is the order creation. It is the entry point of the order flow as there no order flow transition occurs yet.