I'm glad you posted here, @MWCarrie. Yes. A path to find the invoices you created using the client's project number is available via the Transaction List by Customer report. Let me show this to you below.
Before anything else, I'd like to know how you added the Client Information field in the invoice form because this will matter on the report we'll run.
The field won't show in the report if you add it to the Invoice form by renaming the Other option from the Customize Data Layout.
Instead, you can add it in the Additional Info section by going to the customer profile to ensure this field is viewable. Here's how:
- Go to the Customers tab. Select Customer Center.

- Hover your mouse over the customer's name and double-click it.
- Select the Additional Info section and click on the Define fields.

- Add the Client Information field and put a checkmark in the Cust, Vend, Empl, Trans, and List columns.

- Click OK. Then, click OK again from the page.
After that, create an invoice and add the project number in the Client Information field. Once done, find it by running the Transaction List by Customer report and customize it to show the transaction using the client project number. You can follow the steps below:
- Go to Reports, and select Customers and Receivables. Then, Transactions List by Customer.

- Click the Customize Report.
- In the Filters section enter the Client Information in the provided field and click it once it shows. In the other blank column specify the project number.

- Once done, click OK.
I'll also add this article if you want to memorize the report you currently customize: Create, access, and modify memorized reports.
If you want to have more discussion about locating invoice details in QuickBooks Desktop via the Project number information, let us know in the comment section below. We'll respond as soon as possible. Take care, and have a good one.