iPad Air 2 keeps asking for password every time I update - why doesn’t it use Touch ID?

[VA835]

Hi, new here, and I have a question.

I’ve noticed that on my two iPhones (one personal, one for work), when I update apps they normally don’t ask for my Apple ID password.
However, when I update my iPad Air 2, it always asks for the password, even though I have Touch ID set to approve iTunes purchases.
I’ve restarted, to no avail.
Maybe I’m missing something obvious, but have been through the settings several times, and cannot figure it out. Anyone else run into this?

To clarify, I’m running the latest iOS, and this has been an issue for several iterations of iOS.
Thanks

 

[anony_mouse]

This never worked correctly for me on the iPad 3. iOS always asks for my password when updating apps, regardless of what settings I have. I suspect Apple don't bother to test this.