Hello.
In System Configurator - Call Switching - Global Switching Settings there is this setting:
Cause Code for Rerouting Calls -
Define cause codes that make the Call Dispatcher to retry call routing to an alternative destination. Can be used in environments with multiple SIP and H.323 gateways. Different devices use different cause codes for informing about insufficient line capacity or congestion; list the codes here to accurately recognize rerouting needs. Enter a comma-separated list of string values, for example 34,44,58.