BTW, you would use an IFRAME with the src= URL set to:
https://www.e-junkie.com/ecom/rp.php?noredirect=true&txn_id=XXXXX
...(where XXXXX is the txn_id we passed to your page during the redirection), so all your script really needs to do is receive that txn_id value we pass, and then output that value into the appropriate place in the IFRAME src= URL inside your page.
To customize what our thank-you page outputs, please refer to this customization help page (note there are both general and product-specific thank-you page customization fields, each with their own sets of templatable values):
http://www.e-junkie.com/ej/help.customization.php