def add_value(self, value, timestamp=None):
        """ Method for `Update Data Stream Value <https://m2x.att.com/developer/documentation/v2/device#Update-Data-Stream-Value>`_ endpoint.

        :param value: The updated stream value
        :param timestamp: The (optional) timestamp for the upadted value

        :return: The API response, see M2X API docs for details
        :rtype: dict

        :raises: :class:`~requests.exceptions.HTTPError` if an error occurs when sending the HTTP request
        """
        data = {'value': value}
        if timestamp:
            data['timestamp'] = timestamp
        return self.api.put(self.subpath('/value'), data=data)
Method for `Update Data Stream Value <https://m2x.att.com/developer/documentation/v2/device#Update-Data-Stream-Value>`_ endpoint.

        :param value: The updated stream value
        :param timestamp: The (optional) timestamp for the upadted value

        :return: The API response, see M2X API docs for details
        :rtype: dict

        :raises: :class:`~requests.exceptions.HTTPError` if an error occurs when sending the HTTP request