You're on the right track. Let me help share information which can be the reason why your profit and loss in cash report displays your unpaid invoices.
When your profit and loss in cash report, invoices on the said report has been linked to a payment. These invoices can be based on the following statuses:
Closed - paid with the full amount
Partial - paid with part of the full amount but still open
With this, let's open the Transaction Detail view of your Profit and Loss report for the sales income account to review the said invoices. You can do so by clicking the amount of the said account in your profit and loss in cash report.