If a patient is on a treatment program (ie, has purchased and subscribed to a "package"), their invoices will check for this and the invoice amount can be adjusted if required.

In a new invoice screen, if you add a service to the invoice which matches the service name in a subscribed package for the patient, the following prompt will appear.

If you confirm that the patient will be redeeming a service as part of their package, click on OK, and the cost of the service on the invoice will be reduced (to $0.00) to reflect that they have already paid for the service in their package! Otherwise, if you select Cancel from this prompt, the full service price will be added to the invoice.