Good evening dcortes,
Welcome to the Apple Support Communities!
If your Touch ID is working in every app except the iTunes Store, then I would suggest taking a look at the Touch ID settings one more time, and also updating your iTunes billing account information.
I've highlighted some key information here for you. Click on the link for complete details.
Use Touch ID on MacBook Pro
With Touch ID on your MacBook Pro, you can quickly unlock your Mac and make purchases using your Apple ID and Apple Pay—all with your fingerprint.
On MacBook Pro (15-inch, 2016) and later, and MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports) and later, Touch ID (power button) is on the right side of the Touch Bar at the top of the keyboard.
Make iTunes Store, App Store, and iBooks Store purchases with Touch ID
Use Touch ID instead of your Apple ID password to make purchases on your Mac:
- Open the iTunes Store, App Store, or iBooks Store.
- Click the buy button for something you want to purchase. A Touch ID prompt appears.
- Place your finger on Touch ID to complete the purchase.
You might be prompted to enter your password on your first purchase or if you've made changes to the fingerprints that you've enrolled in Touch ID.
Change or remove your Apple ID payment information
If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store