Yes, I usually just upgrade to the next size and pay the difference. As previously said, extra flavoring for $0.50 would count as a purchase to get the free juice reward.
If you just want the free juice you earn then you do have to purchase something even if its just extra shot if flavor (.50 cents)...
Fda regs prevent us from giving away anything completely free, so you do have to buy something, although it can be minimal.
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