Hello Joe!

The invoice currency depends on the currency assigned to the customer profile. If you have a new customer from the US, you can assign USD currency, so their invoice is in USD.

Please note that a currency can only be assigned to a customer when you create their profile. Therefore, the currencies of the existing ones are not changeable. If you assigned the wrong currency, better create a new profile for that customer.

If you have other questions in mind, you can always go back to this thread.