Скорее всего проблемы сертефикатом. Мой код в похожей ситуации:
void SpaceTrackConnection::sendReguest(const QString &request) const
{
QNetworkRequest req(request);
req.setSslConfiguration(d->m_sslConfiguration);
req.setHeader(QNetworkRequest::ContentTypeHeader, QString("application/x-www-form-urlencoded"));
req.setHeader(QNetworkRequest::CookieHeader, QVariant::fromValue<QList<QNetworkCookie>>(d->m_cookieList));
req.setHeader(QNetworkRequest::SetCookieHeader,QVariant::fromValue<QList<QNetworkCookie>>(d->m_cookieList));
auto reply = d->m_networkAcess->get(req);
QObject::connect(reply, SIGNAL(error(QNetworkReply::NetworkError)), this, SLOT(read()));
QObject::connect(reply, SIGNAL(sslErrors(const QList<QSslError> &)), this, SLOT(errorSlotSSL(const QList<QSslError> &)));
QObject::connect(reply, SIGNAL(readyRead()), this, SLOT(read()));
QObject::connect(reply, SIGNAL(finished()), this, SLOT(read()));
}
void SpaceTrackConnection::errorSlotSSL(const QList<QSslError> &erros)
{
auto sender = static_cast<QNetworkReply*>(this->sender());
sender->ignoreSslErrors(erros);
qDebug()<<"ssl errors";
}