Using PayPal Standard, in sandbox, customer downloads not being activated

I'm having a problem (similar to http://www.zen-cart.com/forum/showthread.php?t=118574 ) using Papay Standard for payment and trying to set up for downloadable products.

How can downloadable products not be 'virtual products'? What are virtual products if not non-physical products like downloadable files? And if I set "Shipping Address Required", then Zen Cart does exactly that: displays a shipping address. But the music files I'm trying to deliver certainly won't go to a shipping address.

My problem is that after a successful purchase (using sandbox for now) the user is returned to the "checkout success" page but never gets a download option.

Any help?

mgrobertson:

My problem is that after a successful purchase (using sandbox for now) the user is returned to the "checkout success" page but never gets a download option.I bet they don't get a real order number either do they?
That's a classic case of PayPal's servers not talking to your server to release the order ... a frequent problem for people relying on IPN notifications, which the Standard module requires.

Here's the list of troubleshooting tips: http://www.zen-cart.com/wiki/index.php/PayPal