I've tried to find this in the Forum, the documentation, I've looked at Custom Fields. This is a very simple issue I think.
I simply need to provide a different link per product (they are books) in the email which the users get when purchase is confirmed.
This is because they will go to this link, add their Hikaserial code and download the book.
So it's not a different link for every purchase, just one per book. i.e.
Book 1 - link =
www.book1link.com
Book 2 - link =
www.book2link.com
...etc
Thanks.