A suggested solution that could fix this is to logout and login on the App Store:
1. Open the App Store
2. Go to the Features page.
3. Scroll all the way down to the bottom and press on the button with your Apple ID.
4. Press log out.
5. Restart your device
6. Once restarted, sign back in to your account.
This article from Apple's Support will guide you through the process.
If you are still experiencing any problems, please contact our support team.