docs: def _is_valid_api_url(self, url):
          """Callback for is_valid_api_url."""
          # Check response is a JSON with ok: 1
          data = {}
          try:
              r = requests.get(url, proxies=self.proxy_servers)
              content = to_text_string(r.content, encoding='utf-8')
              data = json.loads(content)
          except Exception as error:
              logger.error(str(error))
  
          return data.get('ok', 0) == 1