add_action( 'woocommerce_email_after_order_table', 'add_payment_method_to_admin_new_order', 15, 2 );

/**
 * Add used coupons to the order confirmation email
 *
*/
function add_payment_method_to_admin_new_order( $order, $is_admin_email ) {
  
  if ( $is_admin_email ) {
  
    if( $order->get_used_coupons() ) {
    
      $coupons_count = count( $order->get_used_coupons() );
    
        echo '<h4>' . __('Coupons used') . ' (' . $coupons_count . ')</h4>';
         
        echo '<p><strong>' . __('Coupons used') . ':</strong> ';
        
        $i = 1;
        $coupons_list = '';
        
        foreach( $order->get_used_coupons() as $coupon) {
            $coupons_list .=  $coupon;
            if( $i < $coupons_count )
              $coupons_list .= ', ';
            $i++;
        }
    
        echo '<p><strong>Coupons used (' . $coupons_count . ') :</strong> ' . $coupons_list . '</p>';
    
    } // endif get_used_coupons
  
  } // endif $is_admin_email
}



add_action( 'woocommerce_admin_order_data_after_billing_address', 'custom_checkout_field_display_admin_order_meta', 10, 1 );

/**
 * Add used coupons to the order edit page
 *
*/
function custom_checkout_field_display_admin_order_meta($order){

    if( $order->get_used_coupons() ) {
    
      $coupons_count = count( $order->get_used_coupons() );
    
        echo '<h4>' . __('Coupons used') . ' (' . $coupons_count . ')</h4>';
         
        echo '<p><strong>' . __('Coupons used') . ':</strong> ';
        
        $i = 1;
        
        foreach( $order->get_used_coupons() as $coupon) {
          echo $coupon;
          if( $i < $coupons_count )
            echo ', ';
          $i++;
        }
        
        echo '</p>';
    }

}