Thanks for helping me on this.

I tried but it still gives me the same error.

I have switcehd between different ports too but teh probelem remains teh same

Web Service URL provides correct response

but Web Portal URL gives HTTP Error 503. The service is unavailable.

This is what i found in logs

2018-08-02 17:44:40.0381|FATAL|1|Could not start PBIXSystem.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Net.HttpListenerException: The network location cannot be reached. For information about network troubleshooting, see Windows Help
at System.Net.HttpListener.AddAllPrefixes()
at System.Net.HttpListener.Start()
at Microsoft.Owin.Host.HttpListener.OwinHttpListener.Start(HttpListener listener, Func`2 appFunc, IList`1 addresses, IDictionary`2 capabilities, Func`2 loggerFactory)
at Microsoft.Owin.Host.HttpListener.OwinServerFactory.Create(Func`2 app, IDictionary`2 properties)
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Microsoft.Owin.Hosting.ServerFactory.ServerFactoryAdapter.Create(IAppBuilder builder)
at Microsoft.Owin.Hosting.Engine.HostingEngine.Start(StartContext context)
at Microsoft.PowerBI.ReportServer.WebHost.Program.Main()
2018-08-02 17:44:40.0381|INFO|1|Logger shutting down