From Nordstrom.com:

Now through Sunday, purchase three nail polishes from Deborah Lippmann or three polishes from butter LONDON, and we’ll automatically deduct the cost of the lowest priced in checkout.

No promo code required.

Online and in store. Excludes sets, top coats and base coats. One per person, while supply lasts. Free nail polish can only be shipped to the same destination as your order and cannot be shipped to PO boxes, military APO/FPO or international addresses.