Launch Settings on your iPhone or iPad
Tap on Touch ID & Passcode
Enter your Passcode or Password
Toggle iTunes & App Store to OFF
Press the Home button to return to the Home screen.
Reboot your iPhone or iPad. (Here's how)
Enter your Passcode or Password at the Lock screen
Launch Settings on your iPhone or iPad
Tap on Touch ID & Passcode
Enter your Passcode or Password
Toggle iTunes & App Store to ON