Assume that you created a new In-process Host and a Host Instance.
Thought you start the host instance, it will not be immediately visible in Send / Receive Handlers of the Send / Receive Ports.
In order for the Host to be visible inside the Send / Receive Handlers, you have to link the Host with the Adapters.
Now, add the Host to the handler.
Now it will be visible in the Send/Receive Handlers.
Hope it helps