A few of you have written in to say Touch ID isn't working to authorize iTunes or App Store purchases, and/or for third party apps, following the iOS 8.3 update.
We've not been able to duplicate the problem on any of our devices, but after helping several people, we have come across what looks to be a working Touch ID fix for those affected. Best of all, it's a simple one!
How to fix Touch ID not working in iOS 8.3
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
That should fix any issues with using Touch ID to authorize App Store or iTunes Store purchases.
For in-app use, remember you may have to enter a password in the specific app before Touch ID will work again in an extension (because your iPhone or iPad rebooted during update). For example, you'll have to launch the 1Password app and enter your Master Password at least once before the 1Password action extension will work with Touch ID in other apps.
With any luck, that'll get Touch ID working again for you in iTunes and App Store, and you'll be happily authorizing away! If you're having the problem, let me know if this fixed you up!