Follow these instructions if you receive a "You need to enable cookies in order to remember this device" with Duo when trying to remember a device using the Safari web browser.
On the Safari menu bar, go to Safari -> Preferences
Double click "Content by Label" below. Under "Labels*" in the left menu, type all labels relevant to this page (those you have added to the page by clicking the "Labels" icon in the bottom left). When finished, delete this comment!