Download links DO NOT come with the email from PayPal. They come in a separate email from eStore, AFTER PayPal sends a valid IPN message back to your site.
Please turn on the eStore debug logs, perform your test, and check for problems in the logs:
https://support.tipsandtricks-hq.com/forums/topic/how-and-when-to-enable-debug-and-what-does-it-do