For some reason I couldn't find the cancel button, honestly had to look for it for a while. My brain expected to be able to click in the top left or right or on the background to dismiss it, never though to look next to the "pay" button. But otherwise the design is awesome!
Yeah, I'd say a big red cancel button (or maybe give the "Pay" button the whole bottom slice, and have a traditional red X button in the corner), and the ability to dismiss the dialog by clicking outside of its frame would go a long way here.
