Hi,
Are you positive that you have a Unity server running properly? the main issue I could see is that you get a rpc failure simply because the network is not properly set.
A User doesn't "create" a server. the server is always running, what a user can do, is becoming the "master" that is deciding on general properties of the application. This is something that takes a bit of time to grasp. If the user that is the current master quits the network, another user is assigned the role of master. this is something also very difficult to apply in practice, so this does require a lot of testing and experience to properly picture who it all fit together to achieve a particular feature.
bye,
Jean