Sales By Customer Detail Report We set custom period (2021 H2) but Open Balance column is showing £0.00 even for invoices paid AFTER the closing date. How to show unpaid?

Hi there, @torturedsoul. I'm here to ensure you'll be able to run a report that shows unpaid invoices.

In the Sales By Customer Detail report, the invoice balance only shows the transactions included in each sale. That may be the reason, the Open Balance column doesn't show any amount.

Meanwhile, you'll want to run the Transaction List by Customer report to view the open balances for each of your customers. This report will also display those paid and unpaid invoices. Let me guide you how:

1. In your QBO account, select the Reports menu.
2. Next, scroll down the Sales and Customers section and click Transaction List by Customer.
3. Then, set the correct Report period.
4. Once done, click the Customise button.
5. Go to the Rows/Columns field and check the box for A/R Paid and Open balance. 
6. Then, select Run report.

Here's the article that will further guide you in modifying your report: Customise reports in QuickBooks Online. 

Also, saving your report customisation is a breeze in QBO. This will allow you to use the same format in the future. 

Keep me posted if you have any other concerns about pulling up a report for unpaid invoices. I'd be glad to assist you once more. Wishing your business never-ending success.