Why isn't sync working correctly for pivot table using many to many

Hey I'm not sure if I'm doing this wrong but I have a many to many relationship and I'm trying to use sync the relationship

using laravel 5.4

Posts.php

class posts extends Model
{
    public function genres(){
        return $this->belongsToMany('App\Genres', 'genres_posts');
    }
}

Genres.php

class genres extends Model
{
    public function posts(){
        return $this->belongsToMany('App\Posts', 'genres_posts');
    }

}

Controller.php

    public function createPosts( Request $r ){
    ...
    ...
    ...

        $post = post::find( 1 ); ;
        $post->genres()->sync(['Comedy', 'Off Topic']);
        ...
    }

genres_posts (pivot table)

|||||||||||||||||||||||||||||||||||||||
|| posts_id || genres_id ||
|||||||||||||||||||||||||||||||||||||||

genres

||||||||||||||||||||||
|| id || name ||
||||||||||||||||||||||

Error

QueryException in Connection.php line 647:
SQLSTATE[22007]: Invalid datetime format: 1366 Incorrect integer value: 'Comedy' for column 'genres_id' at row 1 (SQL: insert into `genres_posts` (`posts_id`, `genres_id`) values (1, Comedy))

Any ideas? (I feel like I'm missing something so blatantly obvious)

Thanks in advance.