This only works if you are a Coke Insider. It takes one Coke cap. Sign into Coke Insider first, then click on this link:https://us.coca-cola.com/insiders-coupon/  

First, log into https://us.coca-cola.com/ and then changed the top url to https://us.coca-cola.com/insiders-coupon/ - I entered one coke cap and it said I would be sent my 12 pack.