App.h

enum class  RESPONSE_STATE {
 
        RESPONSE_RECEIVED_STATE = 0,
        RESPONSE_REQUESTED_STATE,
        RESPONSE_INVALID   

}

class CApp : public QtSingleApplication
{
    Q_OBJECT
    private: 
              //member variables
              RESPONSE_STATE m_eApiCallResponseState;
              QNetworkAccessManager* m_pNetworkManager;

    public:
              CApp( );
              ~CApp();

    public slots:
              void OnClosing();
              void OnResponseReceived(QNetworkReply* pReply);     
};

App.cpp

CApp::CApp ()
              : m_eApiCallResponseState(RESPONSE_STATE ::RESPONSE_INVALID)
              ,  m_pNetworkManager(new QNetworkAccessManager(this)
{
   m_pNetworkManager->setProxy(QNetworkProxy::NoProxy);
   connect(m_pNetworkManager, SIGNAL(finished(QNetworkReply*)), this, SLOT(OnResponseReceived(QNetworkReply*)));
   connect(this, SIGNAL(lastWindowClosed()), this, SLOT(onClosing()));
}

CApp::~CApp()
{
   // Disconnect all the signal slot connection
   // Close all the ports
   // Delete member variables
}

void CApp::onClosing()
{
    m_eApiCallResponseState = RESPONSE_REQUESTED_STATE;
    //I'm making api call here using m_pNetworkManager
    do
    {
    // Checked port is still connected
    }
    while(m_eApiCallResponseState  != RESPONSE_REQUESTED_STATE);
}

void CApp::OnResponseReceived(QNetworkReply* pReply)
{
   //Handle the response
  m_eApiCallResponseState  = RESPONSE_RECEIVED_STATE ;
}

I have made the same api call from other place im getting the response. On making the call from the onClosing(). m_pNetworkManager is not emitting the finished() signal. introduced do while loop just to make sure response is coming or not. Any help is much appreciated.