NOTE: a promo code canNOT be added retroactively, meaning after you have made the order.
Promo codes can be locked to the book type for which they were created. For example, a promo code can be announced as for only one particular book. Or a promo code can be for all three books. So it’s important to read the information carefully for a promo code, which comes out only periodically.
Promo codes can only be limited to a quantity.