Defaults to true. Send false to create the membership as unconfirmed: it is not billed and stays in the "unconfirmed" status until it is confirmed with the Confirm Membership endpoint. The patient is not emailed about an unconfirmed membership at creation; the membership created email is sent when it is confirmed. Practices in a network that requires affiliates to confirm memberships always create them unconfirmed, so the is_confirmed value in the response can differ from the value sent.