@staticmethod
def __parse_reason_503_error(content: bytes) ->str:
    """ Parsing the cause of the error from the server response. """
    html: str = content.decode(encoding='UTF-8')
    body_block = html.rsplit('<body>')[-1]
    reason = body_block.rsplit('<p>Ошибка авторизации: ')[-1].split('</p>')[0]
    return reason
