How can I set the invoice number in the invoice?

I need to generate a sequential invoice number. I've setted the hikashop parameter for the invoice number format this way: {date format="Y"}/{id size="5"} so I can have: 2013/00001

Anyway when I generate the invoice for the vendor I still see the order number in the invoice instead of this 2013/00001

What's wrong?

I've just set the vendor invoice number format in the vendor options this way: {date format="Y"}/{id size="5"} but still I see the order number format instead of this in the new invoices I try to generate.

In the vendor options I cannot see the "Vendor root category". Something misconfigured in my case?

Hi,
I'm missing something...
I don't understand the difference between "Vendor Invoice Number"and "Invoice Number".

I need just a simple number (1, 2, 3, 4...) restarting from 1 each 1 jan /each year.

I understand that Hikashop now has this feature but I don't see any documentation on how to get it out (I've seen the format {id} but I still get a different style).
Is there a way to get control of the order_invoice_number field in order table?
Where this number is generated in?
Thanks in advance!

I've got it.
Changes to invoice number format work only on new invoices as the number is saved formatted..