You can enable Restrictions, also known as parental controls, on iPhone, iPad, and iPod touch. Restrictions stop you from using specific features and applications.
To enable in-app purchases, please use the follow directions.
1) Exit the App and go to “Settings” -> “General”.
2) Scroll to “Restrictions” and tap the “Restrictions” button.
3) You’ll be asked for the passcode which was set to lock certain iOS functions.
4) Scroll down to the “Allowed Content” section and slide the “In-App Purchases” to “On.”
Note: If you lose or forget a restriction passcode, you will need to perform a factory restore to remove it.