Apparently what happens is that it can work sometimes, or sometimes the app just doesn’t open properly, which basically means that it isn’t quite as reliable yet and maybe you shouldn’t be using the Android O beta as your daily driver, especially if you rely on Android Pay rather heavily.
It is possible that Google could address this in future beta releases (we’re assume they’ll definitely address this before Android O’s public release), but for now if you do plan on getting the beta, note that this is a potential problem you could run into. Even Google notes on its beta program, “The updates that you’ll receive as a part of this program are pre-release versions, and may contain errors and defects that can affect normal functioning of your device.”
That being said if you don’t use Android Pay and want to get your hands on the beta, the Android O beta program registration has already gone live so hit up Google’s website for the details.