Thanks for being a member of the QuickBooks family. QuickBooks Online offers a solid projects management feature where you can easily create new projects and manage your business more efficiently. At the moment, moving an already paid invoice to a project is not an integrated feature of the system. Doing so will reopen the invoice and remove the previously applied payment.
If you wish to move an invoice to a project, follow these steps:
Select Sales from the left menu
Select the Invoices tab
Select the invoice you wish to move
Under Customer, select the Project from the drop down menu
Select Save and close from the bottom menu
Once the invoice is moved over, you can reapply the payment accordingly.
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