Maybe a minor software-related bug is the reason why the Touch ID doesn't work for apple pay or in the App store. To fix this, follow the steps below:
Maybe a temporary issue with the app through which you want to make purchases is the reason why the Touch ID doesn't work. Restart the app and try again.
Feel free to consult the don't know how to close (quit) programs/applications guide if you are not sure how to fully close apps.
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.