WooCommerce Pdf Vouchers - Function to solves coupon code already used issue on checkout page

woo_vou_pdf_coupon_hold_stock_on_checkout.php

// add below code to the functions.php of your child theme.

add_filter('woocommerce_hold_stock_for_checkout', 'woo_vou_pdf_coupon_hold_stock_on_checkout');

/**
* Disable the filter
*/
function woo_vou_pdf_coupon_hold_stock_on_checkout(){
  return false;
}