I just moved from an iPhone 6s to Xs. On the 6s if an app (let's say CreditKarma)needed secure log in it would ask for fingerprint ID. On the Xs I'm asked for the phone's PIN. I've looked but cannot find a way have it ask Face ID. I have already turned on Face ID in every place I can find. Also APP Store asks for a double click on the side button instead of Face ID. I do really, really like the phone. Just working out the kinks.