Hi brayb,

Thanks for joining the thread. You can create as many invoices per project in QuickBooks Online. Let me show you how to create invoices linked to a project.

1. Go to Projects tab. 
2. Click on a project on the list.
3. On the Add to project dropdown menu, select Invoice. 
4. Enter details on the invoice and then click on Save.

For more detailed information, you can check these articles:

Set up and send progress invoices in QuickBooks Online

Create and manage projects in QuickBooks Online and Accountant

Feel free to drop a comment below if you have any other questions, we're here to help.