FAQPage structured data for accordion in Gutenberg block template

I´d like to add FAQPage schema in my Gutenberg block, that contais a accordion with questions and anwers.
I´m also using ACF to add the questions and answers repeater into the block.
I´v found a code with a model of what would suit me just fine, but the schema does not work as espected (only this line apears – <script type="application/ld+json">{"mainEntity":null}</script>).
Other problem i´m facing is that as I insert the block into my editing page, it gets publishing error.

this is my edited code for Gutenberg Block with Faq schema:

 <section class="faq accordion-1 section">
  <div class="row">


<?php if (have_rows('faq')) : ?>

  <?php while (have_rows('faq')) : the_row(); ?>

    <h3 class="section-title"><?php the_sub_field('faq_section_name'); ?> (<?php echo count(get_sub_field('faq_section')); ?>)</h3>

    <?php if (have_rows('faq_section')): ?>

    <div class="accordion faq-questions" data-accordion data-allow-all-closed="true">
      <?php while (have_rows('faq_section')): the_row(); ?>

        <div class="question" data-accordion-item>
          <header class="question-header">
            <p class="question-title accordion-title"><?php the_sub_field('faq_question'); ?></p>
            <span class="question-header-toggle"></span>
          </header>

          <div class="question-content" data-tab-content>
            <?php the_sub_field('faq_answer'); ?>
          </div>
        </div>
      <?php endwhile; ?>
    </div><!--  end accordion faq-questions  -->

  <?php endif; ?>

  <?php endwhile; ?>

  <?php 

    $schema = array(
    '@context'   => "https://schema.org",
    'Newtype'      => "FAQPage",
    'mainEntity' => array()
    );

    global $schema;


    if ( have_rows('faq') ) {

    while ( have_rows('faq') ) : the_row();

      if ( have_rows('faq_section') ) {

        while ( have_rows('faq_section') ) : the_row();

          $questions = array(
            'Newtype'          => 'Question',
            'name'           => get_sub_field('faq_question'),
            'acceptedAnswer' => array(
            'Newtype' => "Answer",
            'text' => get_sub_field('faq_answer')
              )
              );

              array_push($schema['mainEntity'], $questions);

        endwhile;

      }

    endwhile;


    function fnz_generate_faq_schema ($schema) {

      global $schema;

      echo '<!-- Auto generated FAQ Structured data --><script type="application/ld+json">'. json_encode($schema) .'</script>';

    }

    add_action( 'wp_footer', 'fnz_generate_faq_schema', 100 );


  }

  ?>

<?php endif; ?> <!-- endif have_rows('faq'); -->


  </div>
</section>