Basically as it say's don't spend anything to amass the money, that was the mistake i made i'm nearly at 48,000,000 keep doing the challenges to get crates which sometimes contain money , there is also a 10 day log in where you get differing amount of crates the most i have had out of 1 crate is 10,000,000 which i have proof of in a game clip, so save don't spend!