If you follow our 2CheckOut integration procedure, our system will automatically issue the download link as soon as 2CO confirms they have completed the buyer's payment:
http://www.e-junkie.com/ej/selling-with-2checkout.htm
After the buyer finishes checkout and 2CO confirms the buyer's payment was good and completed, we grant the buyer access to a thank-you page where we present their unique download link(s) automatically. In case the buyer does not proceed to the download page directly after checkout (e.g., if the payment was put on hold for potential-fraud review), we also issue the buyer a thank-you email with a link to reach the thank-you/download page once their payment is completed. Their download link(s) expire after the number of attempts or hours (whichever comes first) that you specify in each product's settings.
You can also use the "Send free download link" function in your E-junkie Seller Admin to issue a link manually to anyone at any time you choose.