Please note that discounts and promotions are not combinable. This means that only one code can be applied per order. The respective code can be redeemed in the checkout through the "Apply Discount Code" field.
If your discount includes a free product, it is important to also add it to the cart additionally. Please also consider the conditions of the discount or the respective promotion.
If it still doesn't work, please send us a screenshot (screengrab) of the error message along with the discount code through our Service Form. We will strive to find a swift solution. :)