Every time you purchase “Music” from iTunes or purchase or download an app from the App Store, you need to enter your Apple ID password.
iPhone/iPad - How to “Add a Fingerprint” for use with Touch ID
Authenticate iTunes/App Store with Touch ID (fingerprint)
Let’s actually authenticate using Touch ID.
Unlock iPhone iTunes Store and App Store
After that, use your fingerprint to authenticate with Touch ID and the app will start downloading.
