I appreciate you for joining this thread, @bostrav59.

The option to send an invoice without opening your account isn't available in QuickBooks Online (QBO).

You'll need to log in to QBO every time you send an invoice to your customer. This way, we can prevent any security risk with your account and ensure only the owner or authorized user is billing your customer.

Furthermore, I'm attaching this article that you can read for reference in case you want to learn how to customize your invoice: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm just a post away from you if you have other questions about invoices or with QBO. Simply add the details in your reply and I'd be delighted to answer them for you. Have a jolly weekend!