Relationship many to many works only one way

Dear all, I am new to laravel and I have been following the tutorials and in chapter 31 relationships many to many I have an issue and I haven't been able to find a solution

I have defined my relationships in this way: /********* Article.php *********/ '''<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Article extends Model { public function getRouteKeyName() { return 'slug'; }

public function tags()
{
    return $this->belongsToMany(Tag::class);
}

}'''

/********* Tag.php *********/ '''<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Tag extends Model { public function articles() { return $this->belongsToMany(Article::class); } }'''

After populating the 3 tables articles, tags and article_tag with data and testing with tinker I am able to get some results when I use $tag->articles but whenever I use $article->tags it just return null even when the data is there

Does anybody has a clue what should I check?

Thank you in advance for your support Have a good day