How can I search for a particular invoice number?

Hello dgrantcontracts-, thanks for posting on the Community 

You can use the search function in QuickBooks Online to easily locate invoices by transaction number (or on the app, by tapping Invoices on the shortcuts menu > select the Magnifying Glass).

To use the search function on the web, select the Magnifying Glass in the top-right corner of QuickBooks. On the pop-out window, enter the transaction number you’re looking for, then select the desired transaction.

If the transaction you're looking for doesn't appear on the results, try opening QuickBooks in a different web browser to troubleshoot, or select Advanced Search to apply further filters.