Numbers going into negative?

So ive made this game which requires "cobons" as a currency, but the problem i have is they can buy the item, without having the correct funds, let say it costs "200 cobons" the user has 100, buys it, but there currency goes into negative. Does anyone know how to fix this?

Hey Max, in the purchasing event you can add an extra condition - Player cobons is equal to or greater than the purchase price. Otherwise it wont fire.

Thanks , but i dont have players in my game, its a school project based on a remake of adventure capilist, but i will try ur suggested advice