How do they make money on this game

When I got this game I was really looking forward to purchasing gold and cash. Even though it is very expensive, it is still really fun to buy money and purchase weapons. However,every time I would go to the bank section, it would not allow me to purchase the game currency. I tried different things like deleting this app and reinstalling it. It did not work!!! So how do the creators of this game make money off of it if you cant purchase anything. Even though it has its glitches I still enjoy the graphics and idea of this game.

Ajko9 about Contract Killer Zombies 2, v2.0.2