Need help with on screen multiplayer fire button

I am new to unity networking and I am trying to get an on screen fire button click to shoot a projectile. I know that I have to use a command to have the server instantiate the projectile prefab. I have registered the projectile prefab with the lobby manager, but I have no idea how to get the button click to call the fire method. I know I have to be missing something fundamental and have searched the docs and forums to no avail. I have played around with using delegates but I still end up getting the same error on the client: Network server not active. Cannot Spawn objects without an active server. This confuses me since I can see both player prefabs on both the client and the host so I know the server is active. Any help with this would be greatly appreciated.