PHP: CakePHP call to undefined function when importing it from a different Namespace

I’m quite new to PHP and Namespacing. I’m trying to use cakePHP to develop a website and i’m stuck with a problem regarding the use of a function imported from a different namespace.

the problem is the following:

I’ve defined a Class inside a proper namespace called AppPlanner.
The class file is also called Planner.php and it’s locate under src/Planner/Planner.php

<?php

namespace AppPlanner;


class Planner
{
   public static function myfunc(){}


}

Then I’ve got my controller called ChallengesControllerdefined as a class inside a file also called ChallengesController.php under src/Controller/ChallengesController.php which has it’s own namespace AppController. Here I’ve done the following:

<?php
declare(strict_types=1);

namespace AppController;
\ some more imports
use AppPlannerPlanner;

class ChallengesController extends AppController
{

  public function doThings(){
       $res = Planner::myfunc();
  }

}

Now when i call the endpoint /challenges/doThings it reaches the line when i call the function but then gives the following error (i’m using Xdebug to debug):

message = "Call to undefined function AppPlannerknapSolveFast2()"
file = "/var/www/myapp/src/Planner/Planner.php"

my composer.json autoload is set as follow:

 "autoload": {
        "psr-4": {
            "App\": "src/"
        }
    },

can anybody explain to me what i’m missing?

thanks