WordPress使用不起作用的标签加载相关帖子

I'm using a WordPress PHP code to get related posts of a current post, but when i use this code it shows only current post

My code is below

$posttags = wp_get_post_tags(get_the_id(), array( 'fields' => 'slugs' ));

        $args = array( 
                'posts_per_page' => 3,
                'tax_query'      => array(
                    array(
                        'taxonomy'  => 'post_tag',
                        'field'     => 'slug',
                        'terms'     => $posttags
                    )
                )
            );

        $postslist = get_posts( $args );

can anyone help me to get other related posts using current posts tags. Thank You

website url is http://felixwky.com/day-0-experiment/

https://www.google.com/url?q=https%3A%2F%2Fcodex.wordpress.org%2FClass_Reference%2FWP_Query&sa=D&sntz=1&usg=AFQjCNEM20A6MjdZC4XJx7WRhROTOLXSUw refers this link also

 <?php
    //for use in the loop, list 5 post titles related to first tag on current post
    $tags = wp_get_post_tags($post->ID);
    if ($tags) {
    echo 'Related Posts';
    $first_tag = $tags[0]->term_id;
    $args=array(
    'tag__in' => array($first_tag),
    'post__not_in' => array($post->ID),
    'posts_per_page'=>3,
    'caller_get_posts'=>1
    );
    $my_query = new WP_Query($args);
    if( $my_query->have_posts() ) {
    while ($my_query->have_posts()) : $my_query->the_post(); ?>
    <a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a>

    <?php
    endwhile;
    }
    wp_reset_query();
    }
    ?>