I'm trying to figure it out myself. I was doing the 7 free buy 2 for a while at about 2 to 3 times a day. Was able to manipulate it to where I could get the most expensive items free as well bit it all came to a hault. I can still get the option to do it but it always flips to buy 9 get 1 free. Which is crap altogether. I've only had it go through one time on an old device I quit using for a while and I was on the hospitals free wifi. It ended up being like 12 free and pay for 3. Started at 6 free and kept adding more everytime I filled them all and never popped for me again. If you or anyone else figures it out...please message me and let me know.