I'll be more than happy to provide some clarification about your customer's invoice. QuickBooks Online uses e-Invoicing, meaning the form is stored online and accessed through a link provided to the customer in the email you send them. This way, whenever you make updates to the invoice in QuickBooks, the cloud-hosted form is updated as well for immediate viewing.
All you'll need to do to track the invoice's updates is include yourself as a CC in the emailed form. The steps below will help you get started:
CC yourself a copy of your customer's invoices
From QuickBooks Online, click the Gear icon (⚙) and select Account and Settings.
Navigate to the Sales tab and click in the Messages section.
Under Copy (Cc)/Blind Copy (BCc) new invoices to address, enter an email address where you'd like to track invoice updates.
Click Save and then Done.
I'm including a brief video example below for your convenience:
By doing this, you can always check the emailed invoice link to verify that the updates you're making in QuickBooks are visible to the customer. We also offer a guide on customizing invoice emails that you may find helpful. Please touch base with me here if there's anything else you need, I want to ensure your success. Thanks for coming to the Community, wishing you and your business a happy holiday season.