Hello, Eric! I'm sorry for the lag in my response. To clarify:

I don't know if I need a mod or not.
All I know is that I'm supposed to add the piece of code (javascript) to the html header on the purchase confirmation page.

So is there an existing file that I would just add it to?

If not, how do I go about getting that code somewhere so that it will be read as the head of that page?

Thanks so much for all your help!