FOX - Currency Switcher Professional for WooCommerce

Plugin link: https://woocommerce.com/products/smart-coupons/

• In file wp-content\plugins\woocommerce-smart-coupons\includes\class-wc-sc-coupon-process.php add next code:

  if (class_exists('WOOCS')) {
      global $WOOCS;
      if ($WOOCS->is_multiple_allowed) {
          $order_currency = get_post_meta($order_id, '_order_currency', true);
          $rate = get_post_meta($order_id, '_woocs_order_rate', true);
  
          if ($order_currency != $WOOCS->default_currency) {
              $currencies = $WOOCS->get_currencies();
              if (!$rate) {
                  $rate = $currencies[$order_currency]['rate'];
              }
  
              $coupon_amount = $WOOCS->back_convert($coupon_amount, $rate, $currencies[$WOOCS->default_currency]['decimals']);
          }
      }
  }