The Android Pay APK is out there, available for public consumption. Getting it is as simple as heading over to APK Mirror (and making sure you have the right version of Google Play Services installed). Just don't have the Android Marshmallow developer preview flashed to your device. That will bring everything to a screeching halt.
We already knew that you could not set up Android Pay on a rooted device, as this interferes with the app's verification process (though you can re-root shortly after with some success). But we and many other experimental types have found that attempting to launch the Android Pay app on Android Marshmallow brings up a similar error, regardless of whether the device is rooted.
Did this slip by Google? No, as it turns out. An employee reached out to a user on Google+ confirming that Android Pay's system verification will not work in the developer preview, but that it will work just fine in Marshmallow's final release.
Google hasn't provided much in the way of details, but we speculate that Android Pay is using an API from Play Services called SafetyNet. It compares several aspects of your device and firmware to known-good firmware from OEMs to determine if it's original or not. In the case of tampering, it refuses to complete the setup process. We may have more on this as we continue to investigate.
But for now, that, as they say, is that.
- Pranjal Desai