Can you help us with some details of the closed invoice please.

I can share some information that can help you check the details of the closed invoice, @salesegy-seasona.

Would you please provide further information regarding the minus or the negative amount of the invoice to which you are referring? A screenshot will be a great help in identifying this concern, so I can provide you with an accurate answer to this query.

When you open the invoice, click the More button at the bottom of the page to select Transaction Journal to show debits and credits for each transaction to view the amounts and accounts not visible from the transaction itself.

You can refer to this article for more information on how to locate transactions in your account history so you can review or edit them: Find, review, and edit transactions in the account history in QuickBooks Online. 

From here, you can run the Customer Balance Summary report to view the remaining balance for the customer. You can refer to the following article on how to generate and customise this report: Run reports in QuickBooks Online.

Stay in touch if you need further help by leaving a comment below. I'm always glad to assist in any way I can.​ Have a great rest of the day!