WooCommerce PDF Product Vouchers: Display any voucher numbers on the order emails

functions.php

<?php

// Add the following to the end of your theme's functions.php
// Add the following to the end of your theme's functions.php
add_action( 'woocommerce_email_order_meta', 'wc_pdf_product_vouchers_email_voucher_numbers', 10, 3 );

function wc_pdf_product_vouchers_email_voucher_numbers( $order, $sent_to_admin, $plain_text ) {
	if ( class_exists( 'WC_PDF_Product_Vouchers_Order' ) ) {
		$vouchers = WC_PDF_Product_Vouchers_Order::get_vouchers( $order );

		if ( count( $vouchers ) ) {
			echo '<h2>Voucher Numbers</h2>';
			echo '<ul>';

			foreach ( $vouchers as $voucher ) {
				$item = $voucher->get_item();

				echo '<li>';
				if ( $item['qty'] > 1 ) {
					echo $item['qty'] . ' x ';
				}
				echo $voucher->get_product_name() . ' ' . $voucher->get_voucher_number();
				echo '</li>';
			}

			echo '</ul>';
		}
	}
}