How to Fix “In-App Purchase Not Allowed” Message (iOS)

To enable in-app purchases, you need to turn on Screen Time:

1. Go to Settings > Screen Time, then tap Turn on Screen Time.
   
2. Tap Continue, then choose "This is My [device]" or "This is My Child's [device]."
   
   • If you're the parent or guardian of your device and want to prevent another family member from changing your settings, tap Use Screen Time Passcode to create a passcode. Then re-enter the passcode to confirm.
   • If you're setting up Screen Time on your child's device, follow the prompts until you get to Parent Passcode and enter a passcode. Re-enter the passcode to confirm. 
3. Tap Content & Privacy Restrictions. If asked, enter your passcode, then turn on Content & Privacy. 
4. Tap iTunes & App Store Purchases.
5. Tap In-app Purchases and set to Allow.
   

You can also go to Settings > Screen Time > Content & Privacy Restrictions, and tap Allowed Apps. Then deselect iTunes Store and Books.

If the problem persists, please contact Apple Support https://support.apple.com/