Doorbell 2 not functioning properly

Just purchased a ring doorbell 2 and installed it and installed the ring app on my android mobile phone but the doorbell isn’t working properly.
When I push the ring botton on the doorbell it doesn’t ring or send any notification to my phone unless the ring app is open on the phone with live view screen running, otherwise the doorbell won’t work. Moreover, I’m facing the same problem with the motion detection. BTW this is my second doorbell to purchase with the same problem and I tried it on three different mobile phones and still the same.