I've got your back, @tim-swett. I'll make sure you can add an email address using carbon copy in QuickBooks Online (QBO).

You can enter a default email address to avoid entering it each time you create a sales form. Here's how:

1. Go to Settings ⚙.
2. Click Account and Settings.
3. Select Sales tab, then go to Messages section.
4. Select Edit ✎, then enter the default email addresses in the Cc.
5. Click Save, then Done.
   
   

When you create an invoice or other sales forms, you can still edit the email you've added. 

For more information about emailing a sales form or report to multiple email addresses, please refer to this article: Email a sales form or report to multiple email addresses.

You can also personalize the appearance by adding specific info to your sales forms. Check out this article for more information: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm including this article that shows you how to group multiple payments into a single record, track a partial payment, and so on: Record invoice payments in QuickBooks Online.

I'd like to know how you get on after performing these steps, as I want to ensure this is taken care of. Feel free to message me again. Have a great day!