Creating a blank invoice is quite simple and an easy to start fresh for a student. With a blank invoice, you can perform multiple actions such as charge a fee, add a class, and any other functions that are necessary to bill a student. To do so, you would just need to go to the Student Details page of the customer you're creating a blank invoice for. From here, just select the Invoices tab and you'll be brought the option to "Create a blank invoice":
Selecting this option brings you to a blank invoice in order to perform any actions necessary to bill a student: