Display coupon / discount code in invoice PDF

Hi,

I’m trying to display the coupon / discount code used in the order by customizing the “invoice.php” file, but can’t manage to make it work.

I’m able to display the discount amount with order_discount(), but can’t find the function I need to also display the code.

Thanks for you help.

PS: I’m using the free version and that’s the only thing I’m missing…