How do I display the contributor project on the invoice?
In Admin > Setup > Accounting > Invoice Formats, choose to group by project and then select Show Project Code in the Project/Task Display Controls section.
This may be useful if you have multiple contracts/projects within one customer, and want to invoice all of those projects for that one customer on one invoice. You would create a shell or umbrella project as the Lead project, with the other projects as Contributor projects. This shell or umbrella project as the Lead project will have no charges to it, but will be used to group the contributor projects. You may choose to name the Lead project (the shell/umbrella project) with the customer name in the Project Code.