Yes, if the autocomplete list is working then you are ok with your quickfile directory setup.

If the transaction table, hence the log at Drupal, are empty, Quickfile is not inserting de transaction correctly and the download link is generating has no way of confirming it's an approved transaction.

The problem may be related to your IPN setup, if QuickFile doesn't receive a payment confirmed message via IPN it should create at least a "Paypal transaction failed" message in your log. Have you checked that? If you have that message in your log review your Sandbox and IPN setup are correct.

If you don't have anything in your log then take a look at the steps at quickfile_paypal_ipn() in quickfile.module, it's quite possible you will find the source of your problem by knowing what the code is looking for.

Alexis Bellido