Urbackup client on a freenas server

I need a way to backup shares on a FreeNAS server. I’ve created a URbackup server on a Windows PC and can backup all the other PCs but have had no luck backing up the FreeNAS file shares. I cannot find a client for FreeNAS after spending countless hours reading google search results and many of the entries in this repository. Certainly there must be a way to do this. I need a step by step procedure. Assume I know nothing although that is not true. Please be thorough and detailed. My storage devices are 1TB USB GoFlex hard drives connected to the backup server which I rotate on a weekly basis.