How do i link an invoice already sent to a project?

I'm here to help link the invoice to a project, george.

You need to manually link the invoice to a certain project you've created. Please know that any linked transactions attachments will be removed when moving an existing invoice to a project.

For unpaid invoices, here's how to add them to a project:

1. In the left navigation bar, go to Sales, then open the Customers tab.
2. Access the customer profile by clicking on their display name.
3. Find the invoice and open it.
4. Use the Customer ▼ drop-down, then select the project. 
5. Click Save.
   
   

For paid invoices, please browse this link and follow steps 2 and 3 for solutions: Add existing invoices to QuickBooks Online Projects.

I've included a couple resources below which you may find useful:

• Projects FAQ
• Set up & create projects in QuickBooks Online.

You can also browse this link to record deposits made by customers: Learn how to receive and record invoice payments in QuickBooks Online.

Stay in touch with me if you need anything else aside from linking invoices. I'll be around to assist you through the process.