I have noticed an issue with duplicate invoices. The invoice number is not the same however the content of the invoices is identical.

Let me help you figure this out, Liz. This way, we can ensure that your customer transactions are always accurate. 

Do you only see duplicate invoices in the Audit log? If so, what type of user is indicated? You have nothing to worry about if you see the following users underneath as QuickBooks Online (QBO) creates particular users for some specific situations: 

1. Online Banking Administration- This shows a change related to your connected bank accounts made automatically by QuickBooks.
2. Support Representative- Displays changes made by a QuickBooks support consultant.
3. System Administration

• You may see this use if you modify a payment that links to different invoices. 
• You connect a third-party app to QuickBooks. 
•  You create a recurring transaction.
• You set up other events to happen automatically, even when you're not signed in.

    4. Import Administration- There is an automatic change related to converting your data from the QuickBooks Desktop version. 

For more details, see this link: Use the audit log in QuickBooks Online.

But if the duplicate invoice is shown in the reports and one of your colleagues or assistants created it, I'd recommend deleting them. This way, your books will stay accurate. Let me show you how:

1. Go to the Sales tab and select Invoices. 
2. Locate the duplicate transactions.
3. Click the small drop-down arrow under Action and pick Delete. 
4. Hit Yes. 

Additionally, check out these articles below on how to send invoice reminders and record customer payments in QuickBooks: 

• Record invoice payments in QBO
• Send invoice reminders automatically or manually in QBO

Please know that you're always welcome to comment below if you have other concerns or follow-up inquiries about monitoring your transactions in QBO. I'm just around to help. Take care always.