What if you implement in-app purchases. It will look like a free program, but when they get used to it: "Bang! You have used all your id-card-coins for the week

What if you implement in-app purchases. It will look like a free program, but when they get used to it: "Bang! You have used all your id-card-coins for the week. Would you like to buy more?". This is how consumers are owned these days and they seem to enjoy it.