I’m trying to display the full size image of the single post from a custom post type that I created, below 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 while ( $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>
</section>

but seems this

get_the_post_thumbnail_url('full')

not working because it shows nothing e.g. src="" but if I do

get_the_post_thumbnail_url()

surely gives me the image url but not the full size one. Any help, ideas please?

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