Users can refund a Service to a patient. When selecting a service the user will be presented with the following screen. Since a Service cannot be returned to the inventory you can only remove it from the line item detail list of the invoice. The Remove Item basically cancels the service.
A user can then create a new service for a different amount if the service is to be only partially refunded. Another option is the service amount can be adjusted using the line item detail amount or a discount can be given essentially achieving the same result. Note that a refund of the amount paid to the patient for the difference of the two amounts paid and adjusted may be required.