code: protected function getErrorMessage($response, $alternativeError = 'Unknown error.')
      {
          $xml = $this->parseResponse($response);
          if ($xml && $xml->Message) {
              return "[" . $response->getStatusCode() . "] " . (string)$xml->Message ."\n" . (string)$xml->AuthenticationErrorDetail;
          } else {
              return $alternativeError;
          }
      }
docs: Get error message from HTTP Response;
  
  @param Beberlei\AzureBlobStorage\Http\Response $response Repsonse
  @param string $alternativeError Alternative error message
  @return string