Set data-src attribute in a function for lazy-loading of image (WordPress)

wp-img-data-src-function.php

function rchv_projects_link() { ?>
  <a class="grid_item-link gallery_item-link" href="<?php the_permalink(); ?>" aria-hidden="true" tabindex="-1">
<?php $imgPlaceholder = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk2A8AAMUAwUPJ2C4AAAAASUVORK5CYII="; ?>
    <figure class="grid_item-figure gallery_item-figure">
       <?php if( !empty(get_the_post_thumbnail()) ) {
          the_post_thumbnail( 'post-thumbnail', array(
            'alt' => the_title_attribute( array(
            'echo' => false,
            ) ),
            'src' => $imgPlaceholder,
            'data-src' => get_the_post_thumbnail_url(),
          ) );
      } else {
          echo '<img src="data:image/svg+xml,%3Csvg xmlns=\'http://www.w3.org/2000/svg\' width=\'1200\' height=\'800\' viewBox=\'0 0 1200 800\'%3E%3Crect width=\'1200\' height=\'800\' fill=\'%23AAA\'/%3E%3C/svg%3E" />';
      }
$img_caption = get_field('img_caption'); ?>
      <figcaption class="grid_item-caption gallery_item-caption"><?php if( $img_caption ): the_field('img_caption'); endif; ?></figcaption>
    </figure>
  </a>
<?php }