Cause I would say you get the olives for every 100 spend in the same transaction. So you would have gotten 2 if you've spend the 240 olives in one transaction or at least 2 transaction beeing 100 olives or above each.
And you're right, it's not written explicit.

I have spent 120 olives and I got 1 bonus gift box. Then I spent another 80 olives resulting in total 200 olives spent, but didnt get any second box. Not even after spending aditional 40 olives...

so 240 olives spent = 1 gift box?

Does anyone else have problems with it?