There really shouldn't be an issue with using it in any store that takes credit/debit cards. To the terminal, it's essentially the same thing as if you swiped your own card.
Maybe it was a connectivity issue? Or the terminal was encased in such a way that the MST signal couldn't reach the reader (That's why slide-in readers won't work, only swipe ones).
I've been using it all week in all kinds of stores and restaurants and so far no issues at all. Love the faces people make when they try to tell you they don't take NFC payments and the phone won't work and then realize that you DID pay with your phone.
