The connection method for 3CX is determined by the firewall rules.
When If the 3CX system is hosted by 3CX themselves, we'll have to set TIM to listen for a connection from the 3CX.
If a 3CX is hosted any other way, we should be connecting to the 3CX system.
For configuration is self-managed, choose the Active connection.
For 3CX Hosted, use the Listening connection
Configuration details for both methods are shown below: