The Purezone app was designed to support phones or tablets running Android 7.1 and up.

Note:  Google Play store ultimately decides whether an App is compatible with or not compatible with an Android OS version. If this occurs, Google Play will drop support for an app for a specific Android OS version and require that you use a phone with a newer Android OS version. 

If you search for the Purezone app in Google Play on your Android phone and the App does not appear, or if the Purezone app stops working and displays an error message that the App is no longer compatible, you will need to either upgrade the OS of your phone or purchase a newer model Android phone.