Hello, @Questns.
Allow me to share additional insights about emailing paid invoices in QuickBooks.
As of now, there isn't an option to automatically send an email notification to the client informing that the invoice was already paid. To be able to send an email, you may follow the steps provided by Mark_R above to open/locate the paid invoice and manually send it to your client.
After, your client will then be able to view the invoice as paid.
I believe the option of sending an email notification automatically to the customers when invoices are already paid is much necessary for you and your business. I'll take note of this and pass along the suggestions to our product engineers. This way, they'll be able to check and work on with this.
To learn more about sending invoices, you may check this article: Send an invoice.
In case you have any other QuickBooks concerns in the future, you can also read our help articles and look for the topic you need: Help articles for QuickBooks Online.
Let me know if you have any other questions about invoices. I'll be always here to help!
