What is the proper way to display the posts featured image

Hello, I am creating a blog page and have setup multiple queries and pagination. The queries and pagination are working. I can see the titles of the posts populating but for some reason i am not seeing the images.

to display the images i used get_the_post_thumbnail_url() in the src if the image tag. Im guessing this may not be the right way to do it as the images are not displaying.

Im hoping I can get an answer here as to the right way to display the images. Any help is greatly appreciated. Here is the code i have so far.

<?php get_header(); ?>

<section class="bu-header-img-container">
    <img src="/wp-content/uploads/2023/09/bdl-life-static-header-9-23-1.jpg" alt="">
</section>

<section class="bu-title-bar-container bu-page-width">
    
    <div class="col-4 bu-title-left-column">
        <h2 class="bu-yellow-title">Travel Inspiration</h2>
    </div>
    <div class="col-8 bu-title-right-column">
        <hr class="bu-black-line">
    </div>  

</section>

<section class="bu-feature-section bu-page-width"> 
    <?php 
        $featurePosts = new WP_Query(array(
            'category_name' => 'travel-inspiration-feature',
            'posts_per_page' => 1
        ));
        if ($featurePosts->have_posts()) :
            while ($featurePosts->have_posts()) :
                $featurePosts->the_post();
                ?> 
                    <div class="bu-feature-post-container">
                        <img class="bu-img" src="<?php the_field('blue-section-feature-img'); ?>" alt="">
                        <hr class="bu-yellow-line">
                        <h2><?php the_title(); ?></h2>
                    </div>
                <?php
            endwhile;
        endif;
    ?>
    <?php 
        $secondaryPosts = new WP_Query(array(
            'category_name' => 'travel-inspiration-secondary',
            'posts_per_page' => 1
        ));
        if ($secondaryPosts->have_posts()) :
            while ($secondaryPosts->have_posts()) :
                $secondaryPosts->the_post();
                ?>  
                    <div class="bu-secondary-post-container">
                        <img class="bu-img" src="<?php get_the_post_thumbnail_url(); ?>" alt="">
                        <hr class="bu-yellow-line">
                        <h2><?php the_title(); ?></h2>
                    </div> 
                <?php 
            endwhile;
        endif;
    ?>
        
</section>

<section class="bu-posts bu-page-width">
    <?php 
        $ourCurrentPage = get_query_var('paged');

        $mainPosts = new WP_Query(array(
            'category_name' => 'travel-inspiration',
            'posts_per_page' => 12,
            'paged' => $ourCurrentPage
        ));
        if ($mainPosts->have_posts()) :
            while ($mainPosts->have_posts()) :
                $mainPosts->the_post();
                ?> 
                    <div class="bu-post">
                        <img src="<?php get_the_post_thumbnail_url(); ?>" alt="">                        
                        <hr class="bu-yellow-line">
                        <h2><?php the_title(); ?></h2>
                    </div>
                <?php
            endwhile;
            ?>
            <div class="pagination-container">
            <?php
            echo paginate_links(array(
                'total' => $mainPosts->max_num_pages
            ));
            ?>
            </div>
            <?php
        endif;
    ?>
</section>

<section class="bu-page-width bu-pagination-container">
    <img src="pagination-img.png" alt="">
</section>

<section class="bu-page-width bu-bottom-img-links-container">
    <div class="bu-bottom-img-links-left">
        <h2>Book Now</h2>
    </div>
    <div class="bu-bottom-img-links-right">
        <h2>Parking<br>Options</h2>
    </div>
</section>

<?php get_footer(); ?>