Invoices have a few settings you can configure. To see the configurable settings, go to:

Settings & Admin > Feature Settings > Invoices
This can only be done by site admins

On this page, you can change the next invoice number, and the accepted currency.

If the currency you need isn't available in the list, you'll need to go to:
Settings & admin > feature settings > store settings > currency settings,
and change the enabled currencies on that screen.

Note: The invoice number field only accepts integers.

When you're done, remember to save the configuration.