get_the_post_thumbnail_url(‘full’) returns empty from customized put up sort

I am making an attempt to show the total measurement picture of the only put up from a customized put up sort that I created, beneath is what I’ve tried

<?php
 $args = array(
    'post_type' => 'press',
    'order'         => 'ASC',
    'post_status'   => 'publish',
    'suppress_filters' => false
    );
$press = new WP_Query( $args );

if ( $press->have_posts() ) { ?>
    <?php whereas ( $press->have_posts() ) : $press->the_post(); ?>
    <div class="col-sm-4 mb24">
        <article class="post-article bg-white">
            <div class="article-img">
                <?php
                if( has_post_thumbnail() ){
                ?>
                <div class="img-box position-relative overflow-hidden">
                    <a href="<?php the_permalink(); ?>" class="height300 bg-graylight flex-center c-dark position-relative">
                        <img src="<?php echo get_the_post_thumbnail_url('full'); ?>" alt="<?php the_title(); ?>">
                    </a>
                </div>
                <?php } else { ?>
                <a href="<?php the_permalink(); ?>" class="height300 bg-graylight flex-center c-dark position-relative">
                    <i class="ti-image font64"></i>
                </a>
                <?php } ?>
            </div>
        </article>
    </div>
<?php endwhile; ?>
<?php } ?>
        </div>
    </div>
</part>

however appears this

get_the_post_thumbnail_url('full')

not working as a result of it exhibits nothing e.g. src="" but when I do

get_the_post_thumbnail_url()

certainly provides me the picture url however not the total measurement one. Any assist, concepts please?