I also followed the same documentation, and am not getting any notifications. Neither am I getting any errors. I have double checked all the keys and ids, but everything seems in order.
Like Joao, I also noticed that in the Users section of OneSignals, I still have no users registered. But on my Android phones, I have rebooted the app and logged in with several different accounts, yet none of them seems to have registered.
Did anyone else find a solution to this?