Open the Address book of a TrueConf client application and call that H.323 endpoint:
3.2.4.2. How can a TrueConf User Invite a Polycom User to a Group Conference?
Method № 1. Creating a conference on the TrueConf Client application side.
Enter the menu for creating a group conference in the client application TrueConf Client, add a Polycom
H.323 endpoint user to the participants list and click Start: