Hi,
If the product is linked with a pack, HikaSerial will generate serials depending the ordered quantity.
But if your configuration does not allow HikaSerial to access to enough serials or to generate them ; HikaSerial won't be able to perform the assignation correctly.
So, we will need more details about your configuration in order to understand your issue.
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.