Hi,
When you edit the order additional, you can specify a coupon code but it won't find for a coupon code in HikaShop.
It means that you also have to specify the coupon price with the coupon code ; to set the discount for the customer on the order.
It also means that you can write whatever you want for the coupon code, even if the code does not exists in HikaShop.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.