Proxy Authentication error

[amohar]

I an running the following code on windows/qt 5.15.2 and see 407 Authentication error on proxy side while the signal don't get invoked on the client side:
mManager = new QNetworkAccessManager(this);

			mProxy = new QNetworkProxy(QNetworkProxy::HttpProxy,
									   proxy_url, proxy_port,
									   proxy_user, proxy_password);
			

			connect(mManager, &QNetworkAccessManager::proxyAuthenticationRequired,
					this,	  &VplRequest::slotProxyAuthentication);

			mManager->setProxy(*mProxy);
			QSslConfiguration config;
			config.setProtocol(SECURE_PROTOCOL);
			mManager->connectToHostEncrypted(host_url, port, config)

what might be wrong? Thanks.