EU Invoicing: Paid invoices don't generate a separate numeration
When you have chosen EU Invoicing Method under General settings → Billing → Invoicing Method, paid invoices should generate a separate numeration.
Such action is possible ONLY when you add transaction to the invoice.
Note
Changing invoice status manually to Paid doesn't tell HostBill that the invoice has been actually paid, so the system won't generate a separate numeration for such invoice.
When using manual transactions - like Bank Transfer Payment, please apply payments through Invoice → Add Payment menu (button at the bottom of the invoice page):