If you are trying to access this outside of the network the machine you are connecting to is on, you need to set up a static route, or port forwarding, on the main router or firewall to direct the traffic coming in on that port to the address of the machine. Without this, the entire network will receive the request and not know where to direct it.
Good example is an FTP server. If you have an FTP server on your network, anyone on that network can access it, as you are directly accessing it via the IP or hostname of the server on that network. Now if you want to access this FTP server outside of the network, there is no direct route to the server itself, as you are actually connecting to the entire network using it's external IP. When the network receives the communication on port 23 (default ftp port) the routing system has no idea where to send the information on the internal network, as such, the routing system needs to have port 23 forwarded to a specific internal IP, that of the server.
Now, I know you aren't dealing with FTP, however you are dealing with a type of server. All servers of any type need to have outside traffic routed/forwarded to it's appropriate destination.
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