Can you tell the difference between a customer or someone copied viewed the invoice?

Welcome to the QuickBooks Community, @account14.

Can you please provide more information on what you are referring to with regard to "someone copied viewed the invoice?" Any additional information would be greatly appreciated. This way, we can provide the best resolution for your concern.

As always, feel free to visit our QuickBooks Community help website if you need tips and related articles in the future.

Keep in touch if you need any more assistance with this, or there's something else I can do for you. I've got your back. Have a good day!

This is the behavior if you set up electronic invoicing, account14.

Once you turned on the online delivery, those email recipients which include any CC and BCC will show the invoice status as viewed by the customer. The same goes for when you're using an app. 

Since we're unable to track specifically as to who opened the invoice, you'll want to send the invoice directly to your customer first. Then send a separate email to the email recipients.

Please check this article for more information: Track The Status Of Your Invoices In the QuickBooks Online App.

For future reference, you can check payments made to QuickBooks Online by running a report. Please read this article for more information: Run Reports In QuickBooks Online.

Fill me in if you need anything else. I'm always here to help.