Products and Categories discount don't apply

I'm trying to create a discount of 15% to a specific category (I tried also on a specific SKU) but when applying it dos nothing.
I did this:

1) Assigned to categories
2) Checked Use Percentage
3) Inserted 15
4) Marked Requires Product code
5) Inserted Coupon code
6) Saved
7) Set Minimum order total = 0
8) In Applied to Categories, selected the specific category I'm interested the discount to applied

In front office I inserted test product, on checkout inserted the code and the discount doesn't apply.
Any ideas?
Thanks

I do not understand purpose of step below:

infinito62 wrote:

Without that step, discount would be working fine.

I made other tests and it works.
The problem is that if you apply a discount and remove it, it will not apply untill you flush the server cache. So every time you change the coupon status, changes do not apply.
IThis is a bug, if you apply a codeand remove ir, it is aìexpected to work like a toggle, not to do nothing just because the cache isn't updated.

none of the suggestions seemed to work for me in this thread or any of the others. Instead i was able to get this to work by changing the applied discount category from unpublished to published.

hope this helps