with lightbox

Hello! thank you for this nice plugin.

my theme use lightbox for featured image. I want lightbox apply to second featured image,too.

this is code for my original featured image.

<div class="post-image lightbox overlay">
   <a href="<?php echo $original_image_url[0]; ?>">
     <?php the_post_thumbnail('large'); ?>
     <span class="overlay-block"><span class="overlay-icon"></span></span>
    </a>
</div>

For second featured image, I duplicated it and replace image part with code you gave.

<div class="post-image lightbox overlay second-featured-image">
    <a href="<?php echo $original_image_url[0]; ?>">
      <?php if( class_exists( 'kdMultipleFeaturedImages' ) ) {
         kd_mfi_the_featured_image( 'featured-image-2', 'post' );} ?>
      <span class="overlay-block"><span class="overlay-icon"></span></span>
    </a>
  </div>

I have no problem to display second image, But when I click second image, It links to first image in lightbox. Maybe this is natural result, I know nothing about coding…
how can I get right result?

Sorry for my bad english, Any help would be appreciated..

http://ww.wp.xz.cn/extend/plugins/multiple-featured-images/