With the fingerprint sensor being Apple’s big selling point for iPhone 5s, Apple wanted things to be as smooth as can be so that this new technology used in their phones is accepted and commended by the users. Unfortunately, some users found that the Touch ID did not work properly for iTunes purchases. Apple quickly fixed the problem with an update so make sure that you are using iOS 7.0.1 or higher to avoid the problem.
- Go to the Settings menu of your phone
- Tap on General
- Tap on Software Update
If an update is available, then install the latest updates, if not then your phone is using the latest iOS version.
You can also check for updates by plugging your phone to a computer via a USB and go to Devices for your phone and then tap on Check for Update.