How to synchronize 6 topics

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We give 6 topics to sensorsync.cpp code directly. But This code prints only this how to solve this?

void sync_callback(const PointCloud2::ConstPtr& lidar, const ImageConstPtr& image, const can_stdConstPtr &can, const ImageConstPtr& FOV, const GazePointConstPtr& gaze, const NavSatFixConstPtr &xsense)
{ 
    ROS_INFO("Time synced");
}


void second_callback(const PointCloud2::ConstPtr& lidar, const ImageConstPtr& image, const can_stdConstPtr &can, const ImageConstPtr& FOV, const GazePointConstPtr& gaze, const NavSatFixConstPtr &xsense)
{
    lidar_pub.publish(lidar);
    camera_pub.publish(image);
    can_pub.publish(can);
    fov_pub.publish(FOV);
    gaze_pub.publish(gaze);
    xsense_pub.publish(xsense);
}
int main(int argc, char** argv)
{
    ros::init(argc,argv,"sensorsync");
    ros::NodeHandle nh;
    image_transport::ImageTransport it(nh);
    //message filter를 통해 subscribe 해주는 과정 
    message_filters::Subscriber<PointCloud2> lidar_sub(nh,"/livox/lidar",1);
    message_filters::Subscriber<Image> image_sub(nh,"/zed/zed_node/rgb/image_rect_color",1);
    message_filters::Subscriber<can_std> can_sub(nh,"/msg_k",1);
    message_filters::Subscriber<Image> fov_sub(nh,"/FOV",1);
    message_filters::Subscriber<GazePoint> gaze_sub(nh,"/gaze",1);
    message_filters::Subscriber<NavSatFix> xsense_sub(nh,"/gnss",1);
    lidar_pub = nh.advertise<sensor_msgs::PointCloud2>("lidar_sub2",1);
    camera_pub = it.advertise("camera_sub2",1);
    can_pub = nh.advertise<kaaican::can_std> ("can_sub2",1);
    fov_pub = it.advertise("fov_sub2",1);
    gaze_pub = nh.advertise<tracker::GazePoint> ("gaze_sub2",1);
    xsense_pub = nh.advertise<sensor_msgs::NavSatFix> ("xsense_sub2",1);

    typedef sync_policies::ApproximateTime<PointCloud2,Image,can_std,Image,GazePoint,NavSatFix> MySyncPolicy;
    Synchronizer<MySyncPolicy> sync(MySyncPolicy(10),lidar_sub, image_sub, can_sub, fov_sub, gaze_sub, xsense_sub);
    sync.registerCallback(boost::bind(&sync_callback,_1,_2,_3,_4,_5,_6));

    sync.registerCallback(boost::bind(&second_callback,_1,_2,_3,_4,_5,_6));


    ros::spin();

    return 0;

This is my sensorsync code(cpp)