Get the first sub-field from a flexible content field.

get-first-flexible-content-field.php

      <?php 
      // If the page has Flexible Content:
      if(get_field('flexible_main_content')) :
        $rows = get_field('flexible_main_content'); 
        // Get the first instance of the Body Copy field
        foreach( array_slice($rows, 0, 1) as $row ) {
          $excerpt = $row['body_copy'];
          echo '<p>' . trunc($excerpt, 15) . '</p>';
        }
      // Otherwise get the content
      else: ?>
        <?php the_content(); ?>
      <?php endif; ?>