Hello,
If you have already your coupon block in your checkout, reproduce this settings screenshot (by adapting it here or there to your needs of course, dates, discount, category etc!).
As a result you should see this:
If everything is define as showed in my elements, your coupon should normally produce the same effects, IF the conditions/restrictions comply with the contexts, products, dates but also and above all the ACLs, because if your test account does not correspond to defined ACLs then the coupon will not appear.
Regards