<?php if ($block->isDefaultBilling()): ?>
        <div class="message info">
            <span><?= $block->escapeHtml(__("It's a default billing address.")) ?></span>
        </div>
    <?php elseif ($block->canSetAsDefaultBilling()): ?>
        <div class="field choice set shipping">
            <input type="checkbox" id="primary_billing" name="default_billing" value="1" class="checkbox">
            <label class="label" for="primary_billing">
                <span><?= $block->escapeHtml(__('Use as my default billing address')) ?></span>
            </label>
        </div>
    <?php else: ?>
        <input type="hidden" name="default_billing" value="1">
    <?php endif; ?>
      <input type="hidden" name="default_billing" value="1" />
  <?php endif; ?>

<?php if ($block->isDefaultBilling()): ?>
        <div class="field choice set billing">
            <input type="checkbox" id="primary_billing" name="default_billing" value="1" class="checkbox">
            <label class="label" for="primary_billing">
                <span><?= $block->escapeHtml(__('Use as my default billing address')) ?></span>
            </label>
        </div>
    <?php elseif ($block->canSetAsDefaultBilling()): ?>
        <div class="field choice set billing">
            <input type="checkbox" id="primary_billing" name="default_billing" value="1" class="checkbox">
            <label class="label" for="primary_billing">
                <span><?= $block->escapeHtml(__('Use as my default billing address')) ?></span>
            </label>
        </div>
    <?php else: ?>
     <input type="hidden" name="default_billing" value="1" />
  <?php endif; ?>