Eloquent Many To Many Relation Does not return data

I'm trying to make my application with belongsToMany function and pivot Table. I have 3 tables

---forums | ---categories | ---categorie_forum

Forum model: public function categories() { return $this->belongsToMany('App\Entities\Categorie','categorie_forum','forum_id','categorie_id'); }

Categotie model:

public function forum() { return $this->belongsToMany('App\Entities\Forum','categorie_forum','categorie_id','forum_id'); }

In my controller I'm calling following script: public function test(){ $categories = Forum::find(1)->categories(); return response()->json($categories); }

Response return empty json.

What am I doing wrong?