Duo Push is the recommended way to use 2FA if you have a smartphone. This document explains how to check if Duo Push is configured and how to test Duo Push to ensure it is working. Having the Duo Mobile app on your smartphone does not imply that Duo Push is working, so it is a good idea to test in case you need to reactivate Duo Push. If you have a new smartphone since the last time you used Duo Push, you may need to reactivate the Duo Mobile app.