When purchasing a Buy Items, Get Items Free promotion, your store receipt or order confirmation email will show the unit price of each item pro-rated to reflect the promotion. This is to make it easier if you need to return or exchange your products. For example, if the promotion was Buy 1 Item, Get 1 Free, both products would show a 50% discount.
If the promotion is not working, be sure you have the required number of qualifying items. For example, with a "Buy 3 Items, Get 2 Free" promotion, you would need to have a total of 5 qualifying products in your shopping bag.