I am attempting to develop a module that will send an email to a customer in my Commerce 2 store when that customer’s order’s status is updated to "Completed". I am basing my module off of the example shown in the handbook (https://docs.drupalcommerce.org/commerce2/developer-guide/orders/workflows/react-to-workflow-transitions)

Here’s what I have so far:

File: /modules/custom/tracking_number_email/tracking_number_email.info.yml

name: Commerce Tracking Number Email
type: module
description: Uses an event subscriber to send an email with tracking number to customer after order status has been updated.
package: Commerce
core: 8.x

File: /modules/custom/tracking_number_email/tracking_number_email.services.yml

services:
  tracking_number_email.order_fulfillment_subscriber:
    class: Drupaltracking_number_emailEventSubscriberOrderFulfillmentSubscriber
    arguments: ['@language_manager', '@plugin.manager.mail']
    tags:
      - { name: event_subscriber }

File: /modules/custom/tracking_number_email/src/EventSubscriber/TrackingNumberEmail.php

<?php

    namespace Drupaltracking_number_emailEventSubscriber;

    use Drupalstate_machineEventWorkflowTransitionEvent;
    use DrupalCoreLanguageLanguageManagerInterface;
    use DrupalCoreMailMailManagerInterface;
    use DrupalCoreStringTranslationStringTranslationTrait;
    use SymfonyComponentEventDispatcherEventSubscriberInterface;

    /**
     * Sends an email when the order transitions to Fulfillment.
     */
    class OrderFulfillmentSubscriber implements EventSubscriberInterface {

      use StringTranslationTrait;

      /**
       * The language manager.
       *
       * @var DrupalCoreLanguageLanguageManagerInterface
       */
      protected $languageManager;

      /**
       * The mail manager.
       *
       * @var DrupalCoreMailMailManagerInterface
       */
      protected $mailManager;

      /**
       * Constructs a new OrderFulfillmentSubscriber object.
       *
       * @param DrupalCoreLanguageLanguageManagerInterface $language_manager
       *   The language manager.
       * @param DrupalCoreMailMailManagerInterface $mail_manager
       *   The mail manager.
       */
      public function __construct(
        LanguageManagerInterface $language_manager,
        MailManagerInterface $mail_manager
      ) {
        $this->languageManager = $language_manager;
        $this->mailManager = $mail_manager;
      }

      /**
       * {@inheritdoc}
       */
      public static function getSubscribedEvents() {
        $events = [
          'commerce_order.fulfill.post_transition' => ['sendEmail', -100],
        ];
        return $events;
      }

      /**
       * Sends the email.
       *
       * @param Drupalstate_machineEventWorkflowTransitionEvent $event-       
       *   The transition event.
       */
      public function sendEmail(WorkflowTransitionEvent $event) {
        // Create the email.
        $order = $event->getEntity();
        $to = $order->getEmail();
        $params = [
          'from' => $order->getStore()->getEmail(),
          'subject' => $this->t(
            'Regarding your order [#@number]',
            ['@number' => $order->getOrderNumber()]
          ),
          'body' => ['#markup' => $this->t(
            'Your order with #@number that you have placed with us has been processed and is awaiting fulfillment.',
            ['@number' => $order->getOrderNumber()]
          )],
        ];

        // Set the language that will be used in translations.
        if ($customer = $order->getCustomer()) {
          $langcode = $customer->getPreferredLangcode();
        }
        else {
          $langcode = $this->languageManager->getDefaultLanguage()->getId();
        }

        // Send the email.
        $this->mailManager->mail('commerce', 'receipt', $to, $langcode, $params);
      }

    }

I am receiving the following error message when this custom module is installed:

ReflectionException: Class
Drupaltracking_number_emailEventSubscriberOrderFulfillmentSubscriber
does not exist in ReflectionClass->__construct() (line 30 of
/home1/mysite/public_html/core/lib/Drupal/Core/DependencyInjection/Compiler/RegisterEventSubscribersPass.php).

If I remove the tracking_number_email.services.yml the error goes away, but the module doesn’t work (to be clear, it doesn’t work whether or not that services.yml file is in place). I assume I have something erroneous in that services.yml file, but I am stuck trying to figure out what is wrong.