ok, back to basics.... do you have Hangouts, Messenger, Google Connectivity, and Project Fi apps installed? For the time being I recommend setting Hangouts to be default SMS app. It has some hidden (beyond answering initial pop up question) Project Fi settings. Once it's up and running you can change it if you desire. I would power down and eject SIM card to make sure it's seated properly. After powering up try again from Project Fi app.