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.