I've wrongly added one customer and send them an invoice as well. How can I delete this customer permanently

I'd be glad to assist you in removing your customer in QuickBooks, @3stars-ecom-solu.

You can make a customer inactive in your QuickBooks Online account. Once deactivated, he/she will be removed from the Customers area, reporting options, and any other place where he or she is listed.

Here are the steps to make a customer inactive:

1. Go to Sales, then select Customers.
2. Find the customer and in the Action column click Make inactive.
3. Select Yes to confirm the request.

Please take note that this isn't a complete removal of their information, as you will still see their previous activity with your company in reports and their transactions will still be available for access. If you have transactions using the deleted customer, it will say Name (deleted), with the name of the inactive customer.

Additionally, you can run the Customer Balance Summary report and customise it in QuickBooks. This will show you the data on how much each customer owes to you. Just go to Reports and search for the Customer Balance Summary report, then click it to open.

Should you have any follow-up questions or concerns, don't hesitate to post again here in the Community or leave a comment on this thread. Take care and have a good one.