docs: def add(self, list_id, email_address, name, custom_fields, resubscribe, consent_to_track, restart_subscription_based_autoresponders=False):
          """Adds a subscriber to a subscriber list."""
          validate_consent_to_track(consent_to_track)
          body = {
              "EmailAddress": email_address,
              "Name": name,
              "CustomFields": custom_fields,
              "Resubscribe": resubscribe,
              "ConsentToTrack": consent_to_track,
              "RestartSubscriptionBasedAutoresponders": restart_subscription_based_autoresponders}
          response = self._post("/subscribers/%s.json" %
                                list_id, json.dumps(body))
          return json_to_py(response)