Why doesn't the save() method work on related models?

Question

Laravel

Did according to the documentation

public function update(Request $request, $id)
    {
        User::find($request->user_id)->roles()->save(['role_id' =>$request->role_id]);
        {
            Session::flash('store', 'Привелегия успешна добавлена!');
            return redirect()->route('users.index');
        }
    }

And there is an error
Why does not work?

Answer 1

Because argument 1 to Illuminate\Database\Eloquent\Realtions\BelongsToMany::save() must be an instance of Illuminate\Database\Eloquent\Model, but an array given.
Always happy to help, no thanks.

Answer 2

Made fun of the author)))
->roles()->create(