I've used those NFC stickers on the parking meters with my Nexus. You don't even need to have the PayByPhone app open or running. When I tapped my phone it automatically launched the app with the parking spot number inputted so I just had to confirm a duration.
Also, if you don't have the app installed, your phone should launch the Play Store to download and install it automatically.
Also, if you don't have the app installed, your phone should launch the Play Store to download and install it automatically.