I’ve got you covered, @Kinsm. I’m here to share information on how QuickBooks invoice works.
Currently, there isn't a dedicated feature in QuickBooks Online (QBO) that allows you to manage or see notifications related to your customers. If you make changes to an invoice, you and your customer won't receive any notifications regarding the modifications unless they revisit the online page.
Here are the steps on how your customer can access the Invoice online page:
- Open the invoice email.
- Click Print or save.

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The customer can see the revised information (for example, the new due date). They can select the View invoice button to see the complete invoice details.

You may want to contact your customers directly to ensure they're aware of the updates you made.
QBO helps you create and transmit invoices that help you get paid faster. To keep records of your sales clear, informative, and connected from start to finish, you can visit the references below:
Please feel welcome to add a reply here or create a new post if you have any other concerns or additional sales-related questions. I’m always here to help, @Kinsm.