Entertainer birthday code

[DanceDanceDance80]

Does anyone know much about these?? I received one by email this morning, I've copied and paste it after logging in to my account then it says code accepted but no money is removed from the final payment

In the past I’ve used these on discounted items but recently when I’ve tried they only seem to work in full price? Could it be that?

I've tried adding a full price item and it doesn't even discount the full price item. It's so frustrating!