Unlocking sale items
So this may be a stupid question but I haven't been able to find an answer anywhere. When I go to the sale page for the red excavation iy says that the third choice of sale is free but it is locked. My question is how does one unlock it? Is it locked behind a level requirement or do u have to buy the other two to get it? If I have to buy the other two that's fine but I dont want to buy the other two if I'm not gonna get the free one as well.