If you offer packages, you will have clients that generally purchase packages exclusively. However, there may be times when your package clients would like to have lessons outside of their package. In this case, you will need to charge them per lesson, as the cost of lessons for student's with a billing method of "Package" is set to $0.
In order to do this, you'll want to use the Cost Override feature to override the customer's billing method when scheduling a lesson and then generate an invoice to bill them for these lessons. You can follow the workflow below to bill package students for individual lessons:
Create services that are different from your package services that will be used specifically for the individual lessons. If you use the same service as the package service, the individual lessons will be deducted from the client's package balance.
Enable the Cost Override feature in the "Cost & Wage Settings" section of the Account Settings page.
When you are scheduling the individual lessons for your package clients, select the service used for the individual lessons and then use the "Service List Price" Cost Override option to assign a cost to the lesson.
In order to bill your clients for these lessons, generate an invoice and use the "Lessons by Date" option to pull the individual lessons onto the invoice.
You can find more information about the differences between package billing and billing per lesson in Teachworks in this article: Package Billing vs. Billing Per Lesson.