When a user has a registered security key, and it is the default method for 2-Step authentication, the Duo prompt may not show the "Other options" link to select an alternate 2-Step authentication method.
To resolve this click the "Cancel" button in the pop-up window.
Pressing the esc key on your keyboard will not work. After pressing the "Cancel" button Duo will display the "Other
options" link.
Once a different option is chosen (e.g. Duo Push), your browser will remember the selected method for subsequent 2-Step authentications.