Related Questions:
How do I change my currency for Invoices?
How do I know which currency is displayed on an Invoice?
Answer:
The Amount Due labels on Invoices will display the Organization’s Currency that is in the Organization General Settings so that the customer knows exactly what they're paying.
The Currency symbol will display along with the currency code in brackets.
To change your Currency:
Click Settings
Click Organization
Click General Settings
In the Language & Region section, click Edit
Edit the Currency and click Save