Laravel fire obeserver on pivot relations

    /**
     * Array of our custom model events declared under model property $observables
     * @var array
     */
 
    protected $observables = [
        'customUpdate',
    ];

    public function customSave()
    {
        $this->fireModelEvent('customUpdate', false);
        $this->save();
    }

public function customUpdate(Model $model)