[L5] Troubleshooting my custom validation rule

Hello there,

I'm having trouble trying to create a new validation rule. I want to use my rule like this :

// app/http/Controllers/ProductsController.php

$validation = Validator::make($data, ['field'=>'required|third-party-code']);
if ($validation->fails()) { /*...*/ }

So I registered a new service provider :

// app/Providers/AppServiceProvider

public function register()
{
    $this->app->register(CustomValidationServiceProvider::class);
}

In my service provider I binded my validation class and registered the validation rule by extension :

namespace App\Providers;

use App\Validators\ProductValidator;
use Illuminate\Support\Facades\Validator;
use Illuminate\Support\ServiceProvider;

class CustomValidationServiceProvider extends ServiceProvider
{
    public function register()
    {
        $this->app->bind('ProductValidator', function($app){
            return $app->make(ProductValidator::class);
        });
    }

    public function boot()
    {
        $this->registerValidationRules($this->app['validator']);
    }

    protected function registerValidationRules()
    {
        Validator::extend('third-party-code', 'ProductValidator@validateThirdPartyCode', 'third party code error message');
    }
}

Finally the validator class :

namespace App\Validators;


class ProductValidator
{
    public function validateThirdPartyCode($attribute, $value, $parameters)
    {
        return $value == 'some value' || $this->thirdPartyExists($value);
    }

    private function thirdPartyExists($thirdPartyCode)
    {
        // fake test for now
        return !empty($thirdPartyCode);
    }
}

When trying to use this new rule as described above, I'm getting the following error :

BadMethodCallException in Validator.php line 3360: Method [validateThirdPartyCode] does not exist.

The end of the call stack :

1. in Validator.php line 3360
2. at Validator->__call('validateThirdPartyCode', array('third_party_code', ' THIRD_PARTY_CODE', array(), object(Validator))) in Validator.php line 517
3. at Validator->validateThirdPartyCode('third_party_code', ' THIRD_PARTY_CODE', array(), object(Validator)) in Validator.php line 517
4. at Validator->validateAttribute('third_party_code', 'third-party-code') in Validator.php line 431

Looks like validateThirdPartyCode() is not called in my ProductValidator class, but in Validator class instead...

As you can see I'm using some code I found in other discussions about the same subject. But I need this extra little help to understand what's wrong here... Any help will be appreciated :)

EDIT : I tried using a closure :

        Validator::extend('third-party-code', function($attribute, $value, $parameters)
        {
            return $value == 'foo';
        });

I got the same "BadMethodCallException", so I think my "extend" is ignored. :/