Here is the diagram illustrating how Out of Band Authentication (OOBA), aka push authentication works

The blue lines tell you how the notification arrives on the user's mobile phone, while the red lines describe how your action of accept/deny reaches the web service that supports OOBA.

You need to meet the following conditions to use OOBA

• Your mobile phone must have an Internet connection
• You must configure the Google Cloud Messaging service (for Android devices) or Apple Push Notification Service(for iPhone) .
• Publish DualShield DPS and SSO if necessary. In most situations, you need to do it, as the protected web service is accessed from outside.