Reverse Invoke BC anyone with experience to share

I am attempting to connect an internal BC via a Reverse Invoke BC to the outside www for http posts.
I however get some errors when I try to invoke a service in the internal BC via http call.
The proxy port and registration port seem to be connected well. but somehow I cannot call the service in the internal BC.

Question: do I need to provide the user id and password for this kind of remote reverse invoke?