External contractors don’t need a full Webex license. If your firewall rules allow, a Jabber user on a guest network can dial the Telepresence endpoint directly for a secure, encrypted point-to-point call.
Check your CUCM Service Parameters for "Enable Telepresence Interactions." Ensure your Jabber clients are on version 12.8 or higher for the best H.265 and screen flow sharing support. cisco jabber for telepresence