By the looks of your code you're doing everything right.
I just tried doing some testing myself and was puzzled why I was getting the exact problem.
What I'm betting on is that you are using the demo sql file, and due to an oversight by myself, the discounts are actually invalid - as in their expiry date has now passed.
If you are using the demo sql file, what you need to do is update the expiry dates of these discounts.
For a quick fix, try running the following sql to update all the demo discounts.
Code:
UPDATE discounts SET disc_expire_date = DATE_ADD(CURDATE(), interval 1 year);
I will update the Github repo soon with the full SQL script.