Hi,
Unfortunately it's not possible.
The eWay gateway ask for an invoice number before the payment, so before the creation of the order ; so the plugin generate a unique code for the platform.
If we change the plugin to call the eWay gateway after the order creation in HikaShop ; if the user enter a wrong card number, he couldn't be redirect to the checkout workflow, he will have to create a new order or to go in his order listing and finish an unfinished order (if that option is activated in your website).
And because that is not very friendly for the customer ; we prefer to stay this way.
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.