How do I create a quick one-time invoice?

If you want to bill a client for a one-time, on-the-go job, you can do so using the Manual Invoice option in the Invoices screen. You still need to create a project for the job and then create a quick manual invoice for it. Or you can create a manual invoice even for an existing project. You do not need to have time or expenses logged on the project to create a manual invoice. Check CORE Help Center for details.