Adding two extra image field in cpt in wordpress

cpt extaintion

<?php

//init the meta box
add_action('after_setup_theme', 'custom_postimage_setup');
function custom_postimage_setup()
{
    add_action('add_meta_boxes', 'custom_postimage_meta_box');
    add_action('save_post', 'custom_postimage_meta_box_save');
}

function custom_postimage_meta_box()
{

    //on which post types should the box appear?
    $post_types = array('slider');
    foreach ($post_types as $pt) {
        add_meta_box('custom_postimage_meta_box', __('More Featured Images', 'bsale'), 'custom_postimage_meta_box_func', $pt, 'side', 'low');
    }
}

function custom_postimage_meta_box_func($post)
{

    //an array with all the images (ba meta key). The same array has to be in custom_postimage_meta_box_save($post_id) as well.
    $meta_keys = array('second_featured_image', 'third_featured_image');

    foreach ($meta_keys as $meta_key) {
        $image_meta_val = get_post_meta($post->ID, $meta_key, true);
        ?>
        <div class="custom_postimage_wrapper" id="<?php echo $meta_key; ?>_wrapper" style="margin-bottom:20px;">
            <img src="<?php echo($image_meta_val != '' ? wp_get_attachment_image_src($image_meta_val)[0] : ''); ?>"
                 style="width:100%;display: <?php echo($image_meta_val != '' ? 'block' : 'none'); ?>" alt="">
            <a class="addimage button"
               onclick="custom_postimage_add_image('<?php echo $meta_key; ?>');"><?php _e('add image', 'yourdomain'); ?></a><br>
            <a class="removeimage"
               style="color:#a00;cursor:pointer;display: <?php echo($image_meta_val != '' ? 'block' : 'none'); ?>"
               onclick="custom_postimage_remove_image('<?php echo $meta_key; ?>');"><?php _e('remove image', 'yourdomain'); ?></a>
            <input type="hidden" name="<?php echo $meta_key; ?>" id="<?php echo $meta_key; ?>"
                   value="<?php echo $image_meta_val; ?>"/>
        </div>
    <?php } ?>
    <script>
        function custom_postimage_add_image(key) {

            var $wrapper = jQuery('#' + key + '_wrapper');

            custom_postimage_uploader = wp.media.frames.file_frame = wp.media({
                title: '<?php _e('select image', 'yourdomain'); ?>',
                button: {
                    text: '<?php _e('select image', 'yourdomain'); ?>'
                },
                multiple: false
            });
            custom_postimage_uploader.on('select', function () {

                var attachment = custom_postimage_uploader.state().get('selection').first().toJSON();
                var img_url = attachment['url'];
                var img_id = attachment['id'];
                $wrapper.find('input#' + key).val(img_id);
                $wrapper.find('img').attr('src', img_url);
                $wrapper.find('img').show();
                $wrapper.find('a.removeimage').show();
            });
            custom_postimage_uploader.on('open', function () {
                var selection = custom_postimage_uploader.state().get('selection');
                var selected = $wrapper.find('input#' + key).val();
                if (selected) {
                    selection.add(wp.media.attachment(selected));
                }
            });
            custom_postimage_uploader.open();
            return false;
        }

        function custom_postimage_remove_image(key) {
            var $wrapper = jQuery('#' + key + '_wrapper');
            $wrapper.find('input#' + key).val('');
            $wrapper.find('img').hide();
            $wrapper.find('a.removeimage').hide();
            return false;
        }
    </script>
    <?php
    wp_nonce_field('custom_postimage_meta_box', 'custom_postimage_meta_box_nonce');
}

function custom_postimage_meta_box_save($post_id)
{

    if (!current_user_can('edit_posts', $post_id)) {
        return 'not permitted';
    }

    if (isset($_POST['custom_postimage_meta_box_nonce']) && wp_verify_nonce($_POST['custom_postimage_meta_box_nonce'], 'custom_postimage_meta_box')) {

        //same array as in custom_postimage_meta_box_func($post)
        $meta_keys = array('second_featured_image', 'third_featured_image');
        foreach ($meta_keys as $meta_key) {
            if (isset($_POST[$meta_key]) && intval($_POST[$meta_key]) != '') {
                update_post_meta($post_id, $meta_key, intval($_POST[$meta_key]));
            } else {
                update_post_meta($post_id, $meta_key, '');
            }
        }
    }
}
?>
//calling them.....

<?php echo wp_get_attachment_image(get_post_meta($post->ID, 'second_featured_image', true), 'medium_large'); ?>
<?php echo wp_get_attachment_image(get_post_meta($post->ID, 'third_featured_image', true), 'medium_large'); ?>