The Georgia Tech policies for your GT Account require you to use Two-Factor authentication, but your account is not set up properly with Duo. This is most likely caused by your employment department, requiring Two-Factor for all of its employees, but your account has not yet been configured.
You will need to visit the Technology Support Center, to get your account initially configured. Subsequent changes can be done via self-service on the https://passport.gatech.edu website under the "Two Factor" menu.
Before visiting the Technology Support Center, it would be helpful to take a look at the pre-visit checklist here: What should I do to prepare for DUO Enrollment?