use Symfony\Component\HttpKernel\Exception\HttpException;
$node_uuid = 'UUID STRING HERE';
try { $node = \Drupal::service('entity.repository')->loadEntityByUuid('node', $node_uuid); $nid = $node->id(); unset($node);
} catch (Exception $e) { throw new HttpException(400, 'Node UUID does not match one in the system.');
}