After Installing, it may be necessary to trust the application.

Navigate to Settings, General, Profile or Settings, General, Device Management
find the Verifi LLC and "trust" that enterprise developer.

Android device must be configured to allow apps from Unknown Sources.

Android protects users from inadvertent download and install of apps from locations other than Google Play (which is trusted). It blocks such installs until the user opts-in Unknown sources in Settings > Security. Note that some network providers don’t allow users to install applications from unknown sources. Some devices require the apk to be installed from the downloads section once the above link is selected.