Looking for notifier to detect the Checkout Success page

I'm attempting to add some code that detects when a customer has successfully completed a purchase. They are actually purchasing an account on another system external to zenCart, so I want to find a place to do the creating.

Notifiers seem like a good idea but I don't see one that captures the successful completion of a purchase.

Is there a suitable Notifier or is there a better way of doing this?

Any help much appreciated.

Unfortunately there are some bugs in how notifiers were implemented in the order class.

This makes it difficult to get information regarding the order passed to the observer.

However there is one notifier point that would be useful.

NOTIFY_ORDER_INVOICE_CONTENT_READY_TO_SEND

this notifier happens just before the order email is sent, so we can guarantee that an order has been created. It also passes the order id to the observer, so this could be used to pull out order information.