Hello,
You'll always have an order number for your orders.
The invoice number is generated when the order is confirmed (CF "invoice" column for the configuration of order statuses).
And the invoice number is displayed in the invoice (also in the order details) ; but in the listing you will have the order number display to keep an homogeneous content.
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.