Hello there, Marybeth. We'll make sure you can access the Invoice Activity feature to help you effectively track your sales transactions in QuickBooks Online (QBO).

When you click an invoice from the Sales menu's Invoices tab, the Invoice Activity side panel will show up instead of a pop-up screen. Please see the screenshot below for your reference.

If you're unable to do so, this system's unusual behavior is likely caused by a browser-related issue. To fix this, we can perform some troubleshooting steps. Let's start by pulling up your QBO account using a private browser (incognito). Here's how:

• Press Ctrl + Shift + N (Google Chrome)
• Ctrl + Shift + P (Firefox)
• Control + Option + P (Safari)

Once signed in, go to the Sales menu's Invoices tab and select an invoice to open the Invoice Activity side panel.

If you're able to do so, return to your default browser and clear its cache. After that, log out and then log back into your account. This will refresh the system and remove older data that causes viewing and performance issues. 

However, if this matter continues, I'd recommend using other supported browsers.

Additionally, you can pull up the Transaction Detail by Account report to show a list of invoices due on a specific date range. Please see this article for the complete guide: Customize report to see invoices due in QuickBooks Online.

You can always get back to this thread if you have other feature concerns or questions about managing invoices in QBO. We in the Community are always ready to help you out.