Coupon NOT on Invoice?

I'm looking at an invoice, and it shows a coupon discount, but no information about which coupon was used.

How do we add the coupon code to the invoice, so we know which coupon was used in each sale?

Hello MissNookie,

We apologize for your inconvenience but we would like to inform you that showing coupon code to the invoice is not available right now, but we will try to bring this functionality in future.

Thank you. That seems like it would be an easy addition.

Thanks for your suggestions, we will try to inculcate this in future on our system.