This is for a digital product.
After paying, the user must receive a unique link to the downloadable file. If two people purchase the same digital product, they should not have the same encrypted link or the link to the original file.
The link must expire after 24 hours or a different time that I set. If the expiration feature will alter your bid, omit it.
The buyer does not have to automatically receive the link. The link can be inserted into a database. As long as the link is in the database, I can handle the rest. How long and how much (if different from your current bid) for the paypal ipn script to be completed?