WooCommerce user email and product meta data issue

Question

with latest woocommerce updates my old code stoped working.

Any ideas how to fix it?

I need to add download links (from meta fields) to some products, that have that field not empty.

                ?></nobr></td>
            <td style="text-align:left; vertical-align:middle; border: 1px solid #eee;"><?php echo $item['qty'] ;?></td>
            <td style="text-align:left; vertical-align:middle; border: 1px solid #eee;"><?php echo $order->get_formatted_line_subtotal( $item ); ?></td>
        </tr>
        <?php
    }

  //mycode started
  global $mailto;
  if ($mailto == 'user'){
    $pen_audio_1 = get_post_meta( $_product->id, 'pen_audio_1', true );
    if ($pen_audio_1){
      echo '<tr style="background-color:#FFCCCC;"><td colspan="3" style="text-align:left; vertical-align:middle; border: 1px solid #eee;">';
      echo 'Audiofile 1: <a href="my_url/'.$pen_audio_1.'">download</a></td></tr>';
    }

    $pen_audio_2 = get_post_meta( $_product->id, 'pen_audio_2', true );
    if ($pen_audio_2){
      echo '<tr style="background-color:#FFCCCC;"><td colspan="3" style="text-align:left; vertical-align:middle; border: 1px solid #eee;">';
      echo 'Audiofile 2: <a href="my_url/'.$pen_audio_2.'">download</a></td></tr>';
    }
  }

//mycode ended

    if ( $show_purchase_note && is_object( $_product ) && ( $purchase_note = get_post_meta( $_product->id, '_purchase_note', true ) ) ) : ?>

1. I changed if ($mailto == 'user'){ to if ( intval($sent_to_admin) == 0 ) {.
2. I don't know how to change get_post_meta( $_product->id, 'pen_audio_1', true );
3. I tried $pen_audio_1 = get_post_meta( $order_obj->get_order_number(), 'pen_audio_1', true ); but it is not working

====================

Finally, I got working code:

  global $sent_to_admin;
  if ( intval($sent_to_admin) == 0 ) {

  $product_id    = $product->get_id();
  $pen_audio_1 = ''; $pen_audio_1 = get_post_meta( $product_id, 'pen_audio_1', true );
  $pen_audio_2 = ''; $pen_audio_2 = get_post_meta( $product_id, 'pen_audio_2', true );

    if ($pen_audio_1){
      echo '<tr style="background-color:#FFCCCC;"><td colspan="3" style="text-align:left; vertical-align:middle; border: 1px solid #eee;">';
      echo 'Audio 1: <a href="my_url'.$pen_audio_1.'">download</a></td></tr>';
    }

    if ($pen_audio_2){
      echo '<tr style="background-color:#FFCCCC;"><td colspan="3" style="text-align:left; vertical-align:middle; border: 1px solid #eee;">';
      echo 'Audio 2: <a href="my_url'.$pen_audio_2.'">download</a></td></tr>';
    }
  }