To enable in-app purchases, you need to turn on Screen Time:
- Go to Settings > Screen Time, then tap Turn on Screen Time.
- 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.
- Tap Content & Privacy Restrictions. If asked, enter your passcode, then turn on Content & Privacy.
- Tap iTunes & App Store Purchases.
- 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/