It's nice to have you in the Community. I'd be delighted to assist you with deleting an invoice in case of duplicates.
Should you encounter a duplicate invoice in QuickBooks Online, you have the options of voiding or deleting it. One advantage of voiding a transaction is that there's a record of it, while the amount is zeroed out. Additionally, a voided transaction can be restored, while a deleted transaction is completely removed. Here's how to void and delete transactions:
Open up the transaction that you would like to void or delete.
Select More at the bottom of the screen and choose Void or Delete.
Click Yes to confirm that you'd like to void or delete the transaction.
The following is a brief video to serve as a visual reference: