The Multicurrency feature is only available on the Large plan.
We integrate with XE.com, the conversion rates update automatically depending on the date of the transaction you are processing. You can choose which currencies to use and setup custom conversion rates on the Multicurrency menu.
To enable the Multicurrency feature and learn how to choose currencies and custom conversion rates, please click here.
Navigate to Sales > Invoices and click on the Create invoice button.
Fill in the details of the invoice making sure to set the appropriate Currency and Rate.