Is working as a doctor in a private hospital that deals with commercial insurance companies considered a sin, and does it make the salary unlawful, given that the nature of the work is purely medical and requires communication with these companies to ensure coverage of patients' treatment costs?

A doctor's salary in hospitals that deal with prohibited insurance contracts is permissible because he receives his wage from the hospital in exchange for medical treatment, and he has no connection to the insurance contracts. He is not prevented from treating patients who are treated at the expense of insurance companies.