Selected IT services allow you to choose to start using Duo BEFORE it becomes required. To opt in, click the Login button at the bottom of the screen and then click "Opt In" on your desired service(s). You can also choose Duo for all available services by clicking "Opt in to Everything".
For services that have desktop or mobile applications like Outlook, Box Drive, and the Teams app, Duo is usually only required with the initial set-up of the application and after changing your password.