If you post the C# code here, I can see some config required to the objectscript code

The sample and the article not used this: 

Set setting = ##class(%External.Messaging.RabbitMQSettings).%New()

Set tClient = ##class(%External.Messaging.Client).CreateClient(setting, .tSC)

If you use only the ObjectScript code to connect Rabbit, you must set some properties into your setting variable:

 set setting = ##class(%External.Messaging.RabbitMQSettings).%New()
 set setting.host = "localhost"
 set setting.port = 5672
 set setting.username = "guest"
 set setting.password = "guest"
 set setting.virtualHost = "/"
 
 

Can you post your C# or NodeJS code here?