I am writing a payment gateway for WP eCommerce (http://www.instinct.co.nz/e-commerce/) The merchant requires the user to be redirected to the merchants website (similar to paypal express I believe). Once the user has completed the transaction (successfully or not) they are redirected back to the transaction results page of WP eCommerce on my website. I want to check if the transaction was successful and display an appropriate message on the transaction results page.
Where do I put my code or what hook should I use so that my code for checking if the transaction was successful is executed on the transaction results page?