Hello Yohi83,
Thank you for reaching out to Apple Support Communities. We are happy to help you!
We understand you would like to use Touch ID for App Store purchases.
We have taken the liberty of providing you with some helpful information:
Use Touch ID on iPhone and iPad
"Make purchases with Touch ID
You can use Touch ID instead of your Apple ID password to make purchases in the iTunes Store, App Store, and Apple Books. Just follow these steps:
- Make sure iTunes & App Store is turned on under Settings > Touch ID & Passcode. If you can't turn it on, you might need to sign in with your Apple ID in Settings > iTunes & App Store.
- Open the iTunes Store, App Store, or Apple Books.
- Tap something to buy. You'll see a Touch ID prompt.
- To make a purchase, lightly touch the Touch ID sensor."
We hope this finds you well!
Cheers!