belkin thunderbolt 3 dock, iMac Pro

Hello... I have a Belkin Thunderbolt 3 Dock (bought from Apple store) and I've plugged it into every available thunderbolt port on the iMac Pro but it doesn't register as being connected. I've changed ports on both the dock and the Mac and nothing. It's powered on and, if I plug my phone on it'll charge the phone but it doesn't 'see' anything I plug into the docking station, eg external drives etc... has anyone experienced anything similar and know how to resolve? thanks