Service cannot reach gateway Status code: BadRequest

I installed on-site data gateway successfully and after installing, I logged in to register gateway but I got the message:   The service cannot reach the gateway. I can confirm that I can access internet from this server (via proxy server) and all ports are open.

Full error message below:

The service cannot reach the gateway.
Request error: Id: 'ddfbb5c2-985c-4638-9bc6-a6dbf6a52e51', Status code: 'BadRequest', Timestamp: '08/10/2016 06:32:28 +00:00', ErrorCode: 'DM_GWPipeline_UnknownError', Detail: ''
at Microsoft.PowerBI.DataMovement.ExternalClient.PowerBIDataMovementClientExtensions.<EnsureSuccessfulDMMSRequest>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at Microsoft.PowerBI.DataMovement.ExternalClient.PowerBIDataMovementClientExtensions.<DiscoverUnifiedGatewayStatusAsync>d__13.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at Microsoft.PowerBI.DataMovement.EnterpriseGatewayConfigurator.ConfiguratorClientExtensions.<DiscoverUnifiedGatewayStatusAsyncRetry>d__a.MoveNext()