I'm also having the same issue, I think INI might be doing some back-end server related maintenance/updates. Their store page was having some issues yesterday due to a server update. If I had to guess they're updating the INI manager servers right now. This is the response to my support ticket about the store website acting funky:
Hello Eric,
Thanks for reaching out to us and apologies for the inconvenience.
Due to a server update by our store provider, this discount code was temporarily disabled. It should now be applied again once you go to check out.
Kind regards,
Sam