Why is woocommerce custom field value not showing?

Question

WordPress

Added custom field for woocommerce. But I can't display it on the site. An error is displayed.

add_action( 'woocommerce_product_options_general_product_data', 'art_woo_add_custom_fields' );
function art_woo_add_custom_fields() {
  global $product, $post;
  echo '<div class="options_group">';// Группировка полей 
   
   // текстовое поле
woocommerce_wp_text_input( array(
  'id'                => '_text_field',
  'label'             => __( 'ISBN', 'woocommerce' ),
  'placeholder'       => 'Текстовое поле',
  'desc_tip'          => 'true',
  'custom_attributes' => array( 'required' => 'required' ),
  'description'       => __( 'ISBN — это международный номер бумажной или электронной книги.', 'woocommerce' ),
) );
   
   
  echo '</div>';
}

add_action( 'woocommerce_process_product_meta', 'art_woo_custom_fields_save', 10 );
function art_woo_custom_fields_save( $post_id ) {
  // Сохранение текстового поля
  $woocommerce_text_field = $_POST['_text_field'];
  if ( !empty($woocommerce_text_field) ) {
  update_post_meta( $post_id, '_text_field', esc_attr( $woocommerce_text_field ) );
//   $product->save();
  }

}

add_action('woocommerce_template_single_price',function(){
    $product = wc_get_product();
    echo get_post_meta($product->get_id(),key '_text_field', single true);
},15)