First you will need to install the Daxtra Sign App on to your smartphone or tablet. Once you have installed the App then enter your YubiKey and press "Get Activation Code". You will then need to enter this code into the confirmation screen of the Daxtra App registration screen.
Android: while on an Android device download this link updated for Android 12 (but it does work with older Android devices) and follow the instructions when you launch it, which will involve entering an Activation Code, which you get from this page below.
In order to install the app on your phone, you will have to select an option to enable you to install apps from non-trusted sites (usually in the Setup security options on most Android phones), PLUS you may need to download a File Manager such as the Astro file manager from the App store and use this file manager to install the Sign In App from there. This is true if you get an error like "could not open file" from Android.
iOS: a fruity package will be available here soon!