How to set a session value in ajax

Hello, it's possible to set a session value directly in ajax?

example: I want to add this key and value in session

Session(['templateType' => $templateType]);

but in Javascript, using ajax

I have this

          $.ajax({
                url: "set_session.php",
                data: { "templateType": {{\App\Enums\TemplateType::PLACE}} }
          });

but I get 404 error