Thanks for checking in with us, PermDude.

As referenced by my peer above, you'll need to customize your invoice template and enter the project name from there. Here's how:

1. Click the Gear icon at the top menu bar and choose Custom form styles.
   
2. Find your default invoice template and click on Edit.
   
3. Go to the Content tab and click the upper part of the template.
4. Tap on Manage custom fields.
   
5. On the Custom fields section, click on Add field.
   
6. Enter the Project Name and hit Save.
   

Once done, the project name will automatically populate whenever you create an invoice.
 

For your reference, you can take a look at this article to help guide you with utilizing your templates in QuickBooks Online as well as on what other information you can add: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Feel free to get back to me if there's anything else I can help you with. I'll be around to keep helping. Have a good day!