Customers cannot download e-books after purchase

-- HikaShop version -- : 2.1.0
-- Joomla version -- : 2.59
-- Browser(s) name and version -- : Firefox,Chrome
-- Error-message(debug-mod must be tuned on) -- : No Orders Found

The customer is educationlaw.org. They sell textbooks for school lawyers. We have a small selection of encrypted e-books. The purchaser does in fact receive the download link via e-mail. But when purchaser clicks on the link, is redirected to an error screen which announce "No orders found." This did not use to happen, and I don't know why it is happening now. Have scoured the forum for related posts but didn't find an answer that matched.
One attached screen shot shows the e-mail with download link. The second attached screen shot shows the error screen.
Have set up a testing demo at educationlaw.org/haihai
Thanks as always for your help, I am happy to give you a temporary login.
-Jim G.