Routing with parametars problem

The namespace uses a backslash.
$routes->add('product/(:any)', 'Namespace\Catalog::productLookup/$1');

https://codeigniter.com/user_guide/incom...aceholders

O M G, I am official retarded for missing this

Tnx a lot for pointing out this stupid mistake. Now it is working yeee

But what is not now clear to me is why my other routes works with wrong slash?
If you look my example form first post you will see that I have all wrong slashes but only one with parameter really throw error, and that is why I didn't notice it before. But still why other routes works?