In your 'Invoices' tab, click on the blue button labeled 'New invoice'.
Enter the details under 'Customer and data' and fill in the 'Invoice lines'.
To select a currency other than your account currency, click 'Show more options' just below your invoice lines.
Here you can select your desired currency under by clicking on the drop down menu next to the 'Currency' option.
The corresponding exchange rate will be automatically entered by Debitoor.
The exchange rates are updated daily.