It's nice to have you here, john139.
Base on the situation given, you'll want to set up a customer with a Euro currency and use this when creating an invoice.
To achieve this, you can follow the steps below:
Then, you can start creating invoice using the newly created customer.
I'm adding this guide to become more familiar on how multi-currency works in QuickBooks Online (QBO).
Drop a comment below if you need more help or other questions. It's always my pleasure to assist. Have a great day ahead.