Error with a custom twig extension

Hello I get this error:

Twig_Error_Syntax: Unknown "fs_addOne" filter. en Twig_ExpressionParser->getFilterNodeClass() (linea 72 de /home/oskar/Webapps/Drupal/fondosciencie/gpc-d8/web/themes/contrib/gpcbreeze/templates/views-view-fields--articulo-figuras.html.twig).

this is my code:

fs_twig_extension.services.yml

services:
  fs_twig_extension.twig.addone:
    class: Drupalfs_twig_extensionTwigExtensionaddOneTwigExtension
    arguments: ['@renderer']
    tags:
      - { name: twig.extension }

src/TwigExtension/addOneTwigExtension.php

<?php

namespace Drupalfs_twig_extensionTwigExtension;

use DrupalCoreRenderRenderer;

/**
 * Class addOneTwigExtension.
 *
 * @package Drupalfs_twig_extension
 */
class addOneTwigExtension extends Twig_Extension {

     
   /**
    * {@inheritdoc}
    */
    public function getFunctions() {
      return [
	      new Twig_simpleFunction(
	        'fs_addOne',
          array($this,'fs_addOne'),
          array('is_safe' => array('html'))
        )
      ];
    }

   /**
    * Add one (+1) to a string.
    */
    public function fs_addOne($string) {
      $number = $string +1
      return $number; 
    }

   /**
    * {@inheritdoc}
    */
    public function getName() {
      return 'fs_addOne';
    }

}

And I try to use it in a views tpl.twig in this way:

{{ fields.delta.content|fs_addOne() }}

But I get the error.

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/4/feed