See the code sample here.
add_action('post_grid_loop_bottom', 'post_grid_loop_bottom_20200614', 10, 2); function post_grid_loop_bottom_20200614($args, $post_grid_wp_query){ $grid_id = $args['grid_id']; $post_grid_options = $args['options']; ?> <div class="item item-52833 skin flat even 0 ">Custom HTML here</div> <?php }