How to : set a task to invoiced

How to : set a task to invoiced

We currently created a statuslabel "invoiced" within the status "closed". But now we want to create a connection between Zoho Projects and Books. If we create a invoice based on a project it gives all the tasks.

That's great but a couple of tasks are allready invoiced within our old invoice system. How can we set a invoice state to a task so it wouldn't show in Zoho Books.