Hello,
The general workflow do not authorize you to do so.
An order can be create without a payment ; like for example with "paypal" when the order is created an afterwards the customer is redirected to the platform so he can pay the order.
He might not pay it at all, but when it will be done, the order will be confirm.
You don't want to refuse the confirmation of the order since the customer just pay it.
So you have to deal with the serial issue afterwards.
If you can know in advance if the serial generation will fail ; you can try to refuse the creation of the order. It will be compatible with all kind of payment plugin and you will be sure that the customer do not pay for something which wont be handle afterwards.
But no, the serial generation must no interact with the order modification ; a paid order must be mark as paid.
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.