unique validation in laravel issue

I have this rule for my members table

 public function rules()
    {
       return [
                'name'=>'required | max:30',
                'lastname'=>'required | max:50',
                'code'=> "numeric|unique:members,code,$this->id"
        ];
    }

when I want update name or lastname I get this error

The code has already been taken.

where is my mistake, thanks

via Chebli Mohamed