Hello,
The workflow you're describing is not possible.
When the order is confirmed and only when it's confirmed, HikaSerial will generate the serial.
And if you're using the "coupon generator", it will also create an HikaShop coupon code in the database (by copying a "coupon template" you have configured).
BUT !
There is no feature or option to generate a coupon before the order is paid and make that coupon published after.
So, I really don't know how your HikaShop & HikaSerial are configured but what you're describing was not possible unless you have perform deep modifications in the core.
Even if HikaSerial is highly flexible, its workflow is very regarding when and how content is generated.
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.