MarketPress Hooks for custom plugin


I am writing a custom plugin linked to MarketPress which creates a customer and invoice record in KashFlow using the KashFlow API to reflect the order. I want it to fire when the customer completes the transaction, to give certainty it has gone through without any problems, and the best place seems to be when the Order Complete page has loaded. Can you let me know if there any hooks I can attach an action to please?