Hi,
In HikaSerial 1.7.4, the serial is not linked with the coupon. It means that HikaSerial can't know when you use the coupon so it can't put any information for the serial.
The serial can't be a "consume" serial, it is not used by HikaSerial, the HikaShop coupon will be used by HikaShop and have his "own life" (it could have a quota > 1).
So if you want to know if the coupon as been used, you have to take a look in the HikaShop coupons, not in the serials.
But for the next HikaSerial release, we are trying to improve that. I am not sure that we will be able to make the full feature for the next release but, I am to finish some improvements (in order to have something more understandable).
Regards,