Do not use a hyphen in the discount code!

I was testing creating a new discount code. My initial test of a discount code with a code: test-code did not work. I was able to create it successfully, but I got an error on the site when trying to apply the code.

Solution: Remove the hyphen. In the above example: instead of “test-code”, used “testcode” and it worked.

http://wordpress.org/extend/plugins/paid-memberships-pro/