Can I open an old invoice as its not letting me do so now?

Hi pcassidy,

Welcome to the community! QuickBooks Online enables you to review and manage every transaction entered into your account. I'll be happy to assist you with this.

Whether your account status is active or inactive (within 365 days), QuickBooks allows you to open all of your invoices. If you're unable to do so, I'd recommend clearing your cache to ensure there's no browser issue causing bugs in the app or software. Here's how: Clear cache and cookies to fix issues when using QuickBooks Online

Another good troubleshooting step for this kind of situation is to navigate in a private/incognito window or use a different browser compatible with QuickBooks Online. This article presents the list of supported browsers: System requirements for QuickBooks Online, Accountant, and QuickBooks Self-Employed

I hope this helps! Feel free to reach out if you have more questions.