php - Wordpress post thumbnail url is not working correctly -

i have issue website built on wordpress.

i'm trying display post thumbnail blog's page it's not working expected...

here :

<?php $loop = new wp_query( array( 'post_type' => 'post', 'posts_per_page' => 9) );                 while ( $loop->have_posts() ) : $loop->the_post();                 $thumbnail = get_field( 'thumbnail' );                 $category = get_the_category();                 ?>                 <a href="<?php echo get_permalink(); ?>">                             <section class="col-lg-4 col-md-6 col-sm-6" style=" background-image:url(<?php echo $thumbnail['url']; ?>);">                                 <div class="article-head">                                     <h2><?php echo the_title(); ?><br><span><?php echo the_time(get_option('date_format')); ?></span></h2>                                 </div>                             </section>                         </a>                 <?php                 endwhile;                  wp_reset_query(); ?> 

so here is... i'm using acf (advanced custom field) plugin add image field called "thumbnail".

<?php echo $thumbnail['url']; ?> 

this supposed give me thumbnail url... current page url http://robeen.ca/blog/. don't understand why...

can guys me ?

get_field() returns object (array of data), url (string), or id (int). can changed in field settings. var_dump() return value see what's inside.

see docs details.