An easy one. Go to your profile: Settings > Profile & Invoice settings.
Open the “Your profile” accordion and scroll down to the “Invoice” section:
You will see the sample of the invoice number in the darker box. Below it there are draggable elements:
- global invoice number (this one counts up with each invoice created)
- client invoice number (this one counts per client invoice)
- client number (you can give your clients numbers of course. This can be used here)
The example will create invoice numbers like:
global invoice nr + client-number