A recognized degree in psychotherapy is a prerequisite for being allowed to work as a psychotherapist. If you want to work independently as a psychotherapist, you also need to be able to bill health insurance companies because many clients are unable to pay for therapy personally.
Doctors with further training in psychotherapy are entitled to bill the health insurance companies directly. Psychological psychotherapists working together with a specialist in psychiatry and psychotherapy can bill the health insurance companies. This form of collaboration is called delegated psychotherapy.