You find round-the-world and other circle fares by entering the same city for the start and ending cities.

If you want to end at a different city, that's fine but the circle fare from the origin back to the origin still applies.

Additionally you should enter city codes (e.g., YTO/Toronto) not airport codes (e.g., YYZ/Toronto Pearson Intl.) although EF is usually fairly forgiving of mixing them up.