public function addConfiguration(ArrayNodeDefinition $builder)
    {
        parent::addConfiguration($builder);
        
        $builder->children()
            ->scalarNode('merchant_id')->isRequired()->cannotBeEmpty()->end()
            ->scalarNode('merchant_password')->isRequired()->cannotBeEmpty()->end()
            ->scalarNode('receiver_email')->isRequired()->cannotBeEmpty()->end()
            ->booleanNode('sandbox')->defaultTrue()->end()
            ->scalarNode('sandbox_url')->end()
        ->end();
    }
public function addConfiguration(ArrayNodeDefinition $builder)
    {
        parent::addConfiguration($builder);
        
        $builder->children()
            ->scalarNode('merchant_id')->isRequired()->cannotBeEmpty()->end()
            ->scalarNode('merchant_password')->isRequired()->cannotBeEmpty()->end()
            ->scalarNode('receiver_email')->isRequired()->cannotBeEmpty()->end()
            ->booleanNode('sandbox')->defaultTrue()->end()
            ->scalarNode('sandbox_url')->end()
        ->end();
    }
{@inheritDoc}