The CUCMBE is ready to relate with PrivateServer using the SIP Trunk, but still it can't until we create the same configuration on the PrivateServer itself.
2.1 Prerequisite
If you came here then all the necessary prerequisites are matched.
2.2 PrivateServer configuration
You can refer to PrivateServer management documentation for creating a proper SIP Trunk. We are going to explain here which specific values need to be set up in order to create it properly.