BW process which starts with BW Facebook Plug-in RealTimeListener activity fails to start with the error information like below:

ERROR [bwEngThread:In-Memory Process Worker-1] com.tibco.bw.core - TIBCO-BW-CORE-500050: The BW process <Process_Name> instance faulted, JobId [bw0a100], ProcessInstanceId [bw0a100], ParentProcessInstanceId [-], Module <Module_Name>, Application <Application_Name>.
<CausedBy> TIBCO-BW-CORE-500062: ProcessStarter or SignalIn activity [RealTimeListener] fault.
<CausedBy> com.tibco.bw.palette.facebook.runtime.fault.FBEventSourceException: TIBCO-BW-PALETTE-FACEBOOK-500021: The RealTimeListener start failed,Error message:Plugin exception in executing real time method. Message = Fail to get message from Facebook response for real time service:
{"error":{"message":"(#2200) Callback verification failed with the following errors: curl_errno = 56; curl_error = Received HTTP code 502 from proxy after CONNECT; HTTP Status Code = 502; HTTP Message = Private address","type":"OAuthException","code":2200,"fbtrace_id":"AG9rog4bl7thTXiQtZ02lKZ"}}-{ProcessStarterActivityName=RealTimeListener, ProcessName=<Process_Name>, ModuleName=<ModuleName>

The BW Facebook Plug-in RealTimeListener activity works as "webhook" application which allows Facebook to call back via the Https protocol for the relevant events.
Thus the callback_url which is configured through the Http connector resource referred by the RealTimeListener activity must be a publicly accessible IP address.
Otherwise the error mentioned above would occur while starting the BW process which starts with BW Facebook Plug-in RealTimeListener activity.