Upgrading SMART Mobile using the desktop app (or directly via the Android APK) does not work from version less than 451 to the latest version. This is due to a change in the security certificate.
The message will be “App not installed”.
The fix is to uninstall SMART Mobile and then clean install the new version.
If you are using SMART Mobile in kiosk mode, then you will need to factory reset the device and follow the initial process again with the new build. Apologies for this inconvenience, it is just the way the system works.
The new certificate will expire in 3 years, so this is not a frequent problem.