There is one major downside to living on the cutting edge... bugs. When you are running a Developer Preview build from Google you know right away that there will be some things that just don't work. Google has made it very clear that this is the case. One of the main functions in the latest developer preview build, Android Pay, is not working on fist boot. Google had recently fixed this problem with an Android Pay app update for the Dev 3 Preview build so I would imagine it would be pretty upsetting to lose the functionality once again in the latest Dev Preview build. It turns out that if you are experiencing this problem after installing Dev Preview 4 there is a pretty easy fix. Simply clear the app's cache. Problem solved Crisis averted.