EndNote Citations -- Not Working

I am using my 2017 MacBook Pro, High Sierra, version 10.13.2 with Pages 6.3.1 attempting to insert an "EndNote Citation," but the option in the menu bar, Insert > EndNote Citation. The "EndNote Citation" is grayed out. After reading other suggestions, I downloaded the appropriate EndNote plugin (3.0), but nothing changed for me.

Please help, or I'll be forced to use my University's desktops with Word.