Comment by fainpul

In game purchases are a dumb thing in itself and need to go away. You can sell add-ons for your game as additional packages, like DLC. Users go to the store (e.g. Steam) and buy an add-on to the game. It's priced like a normal article and you can offer discounts if you want.

If you offer something that cannot be handled like that and absolutely has to be "in game", it's probably because you're trying to extort the players by frustrating them or try to exploit psychological weaknesses to make users pay more than they want to and you should stop that.