The currency posted in your invoices depends on what currency you set for your customers. You can utilize the multicurrency feature in QuickBooks Online (QBO) to change the currency to an invoice. To start, let's turn the feature on.
Go to the Gear icon at the upper-right and click Account and settings.
Under the Advanced menu, select the Currency section
Select your Home Currency.
Turn on the Multicurrency checkbox, then confirm.
Click Save, then Done.
Then, you can assign a currency to your new customers. 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.
Click the Sales menu and click Customers.
At the upper-right, click New customer.
Enter the customer's profile and click the Payment and billing tab.
Select the currency under the This client pays me with dropdown.
You might also want to check out these articles to learn more about this feature: