How to fix “In-app Purchase Not Allowed” message?

If you get hit with a message on your Apple iPhone or iPad that says “Purchase – In-app purchases are not allowed”  when trying to buy purchases from within apps, it may be related to a restriction setting on the device.

1. From the Home screen, swipe over to the screen with the “Settings” icon, then select it.
2. Select “General“.
3. Scroll down and select “Restrictions“.
4. Type your restriction password. If you don’t remember setting a password, ask anybody else who may have had access to the device.
5. Scroll down to the “In App Purchases” option and ensure it is turned “On“.

You can also check for more details at APPLE's official site: https://support.apple.com/en-us/HT204396