Earlier today, Google decided to introduce Android N to the world - which may as well have been announced as Android Nutella - much earlier than we thought they'd announce a new version of the OS. As such, a lot of eager Nexus owners will no doubt have been rushing out to get their hands on the new Developer Preview. For those that have taken the plunge, not only are their lots of new features waiting to be explored, such as the new multi-window feature and fancy new notification shade but also some bugs and known issues. In pre-release software such as this, bugs and such are expected to come along, but there's also something else standing in some people's way; the lack of Android Pay support.
As folks on Reddit have discovered, Android Pay isn't supported on Android N right now. It's also unlikely that Android Pay will work on any further releases of the Android N Preview, either. This is because Android Pay requires the software it's being ran on to pass Google's "Compatibility Test Suite (CTS)". This is a test that certain apps will run in order to check that the version of Android meets the standard Google has set for it to be compatible for all other Android devices. For those running Android Pay in particular, it's likely the test is ran to ensure compatibility with all the base stations and terminals that keep on popping up to support the payments service. There's also of course the issue that lots and lots of bugs are often present in these sorts of pre-releases and there's a chance Google doesn't want users running the risk of any weird behavior arising with their bank accounts.
This presents some users - mostly those in North America - with a choice of either being able to pay for things with their phone or give the latest version of Android a try. A Developer Preview such as this one isn't stable enough or even feature-complete enough to be ran as a daily driver sort of ROM anyway, so those looking to pay for their daily stop at the convenience store would probably have bigger bugs to deal with beyond the convenience that Android pay affords users.