Yes, I know that HikaShop has two numberseries, one for Order and one for Invoice. I have set that up and try to use it, but I see problems.
When Order is created, e-mail template "Order creation notification" is used. This can hold the Ordernumber and I can modifie it.
When I in backend Confirm order, e-mail template "Order status notification" is used. I don't see that this contains the Invoice number?
When I in backend change status to Shipped, e-mail template "Order status notification" is used again.
I simply miss an e-mail template for Invoice.
With current setup, I need to find a way to show Invoice number, if e-mail template is trigged by Confirmed, and don't show it if it's trigged by Shipped.