I have created a 10% off coupon code which gives customers 10% off products in a certain category.
I have created a new order and tested it and it works as intended.
However, when I try to apply the code to orders which are in "Open" or "Quote", it does nothing although say NoticeYour changes have been saved.
I'm not sure why it's not working but I don't want to have to duplicate the orders just to add the code in, but this seems like the most likely workaround?