Elinchrom Skyport Speed Transmitter

As the title says I have a Skyport Speed transmitter. It has a 2.5mm mono jack. I thought to connect it to my Yongnuo 468 ii's PC Sync port. It does not fire. The manual says

"Integrated Hot-Shoe SYNC 2.5 mm Socket. Use the included Sync cable to connect the integrated 2.5 mm Mono Jack socket with the camera or lens PC socket directly."

I am trying to find the reason for the mono jack if not to connect it to an off camera flash? What would be the point of connecting to a camera using a cable when its already in the hotshoe?

This is perhaps to allow backward compatibility with older medium format cameras, which would have been fitted with a 'cold' shoe, or for instance when I had a Canon 10d, if you fitted a trigger in the hot shoe it would always give me an error code and not fire, so I'd slide in a cold shoe (into the hot shoe) and use the PC socket to trigger the transmitter. To trigger the flash, you'll need to get the optional receiver.