Below is a list of action hooks that are available in the WP Express Checkout plugin.
Payment Processing Related
wpec_payment_completed
This action hook executes after a transaction is completed. This can be used to do some additional tasks after a transaction takes place.
Below is an example of how to use this hook
add_action('wpec_payment_completed', 'wpec_after_txn_callback', 10 ,3); function wpec_after_txn_callback ($payment, $order_id, $item_id) { //Do stuff //$payment is the payment data array. //print_r($payment);//Lets see what info is in this array. }