QNetworkReply::ProtocolInvalidOperationError while uploading video to youtube

Question

After the authorization, I have called uploadVideo function. However I have taken QNetworkReply::ProtocolInvalidOperationError. this->mOauth is an instance of QOAuth2AuthorizationCodeFlow. Where do I do wrong? Thanks in advance.

QNetworkReply * Uploader::uploadVideo(){
QNetworkRequest * request = new QNetworkRequest{videoInsertUrl};
request->setRawHeader("Authorization",
                      QStringLiteral("Bearer %1").arg(mOauth->token()).toLatin1() );


auto multiPart = new QHttpMultiPart{ QHttpMultiPart::MixedType };
auto videoPart = new QHttpPart{};

auto video = new QFile{ mFileName };
if (!video->open(QIODevice::ReadOnly)){
    qDebug()<<" cannot to open video file";
    return nullptr;
}

videoPart->setHeader(QNetworkRequest::ContentTypeHeader, QVariant("video/*"));
videoPart->setHeader(QNetworkRequest::ContentDispositionHeader, QVariant("Slug"));

videoPart->setBodyDevice(video);
multiPart->append(*videoPart);

return this->mOauth->networkAccessManager()->post(*request,multiPart);
}