So I am trying to create a custom email for my woocommerce store, that I can use as a payment reminder. I put everything together as follows: one "custom-payment-reminder.php" file, content as follows: <?php /** * Payment reminder Email * * * HOWEVER, on occasion WooCommerce will need to update template files and you * (the theme developer) will need to copy the new files to your theme to * maintain compatibility. We try to do this as little as possible, but it does * happen. When this occurs the version of the template file will be bumped and * the readme will list any important changes. * * @see https://docs.woocommerce.com/document/template-structure/ * @package WooCommerce\Templates\Emails * @version 3.7.0 */ if ( ! defined( 'ABSPATH' ) ) { exit; } class WC_Custom_Payment_Reminder_Email extends WC_Email { /** * Constructor. */ public function __construct() { $this->id = 'custom_payment_reminder'; $this->title = __('Payment Reminder', 'your-textdomain'); $this->description = __('This is a custom payment reminder email.', 'your-textdomain'); $this->template_html = 'emails/custom-payment-reminder-html.php'; $this->template_plain = 'emails/plain/payment-reminder.php'; // Call parent constructor parent::__construct(); // Other settings like 'enabled', 'recipient', etc. can be added here } public function get_default_subject() { return __( 'Zahlungserinnerung Ihrer Bestellung #{order_number} bei {site_url}' ); } /** * Trigger function to send the custom payment reminder email. * * @param int $order_id Order ID. */ public function trigger($order_id) { // Get the order object $order = wc_get_order($order_id); // Set the email recipient(s) if ( is_a( $order, 'WC_Order' ) ) { $this->object = $order; $this->recipient = $order->get_billing_email(); $this->placeholders['{order_date}'] = wc_format_datetime( $this->object->get_date_created() ); $this->placeholders['{order_number}'] = $this->object->get_order_number(); } // Optionally, you can set additional email headers or parameters $this->send($this->get_recipient(), $this->get_subject(), $this->get_content(), $this->get_headers(), $this->get_attachments()); } /** * Get content html. * * @return string */ public function get_content_html() { return wc_get_template_html( $this->template_html, array( 'order' => $this->object, 'email_heading' => $this->get_heading(), 'additional_content' => $this->get_additional_content(), 'sent_to_admin' => false, 'plain_text' => false, 'email' => $this, ) ); } } Then I put an html template for the email in my child theme at woocommerce/emails/custom-payment-reminder-html.php". The content of that file shouldn't be important for this issue as it is identical in both cases. Next I put the following lines in my functions.php: add_filter('woocommerce_email_classes', 'add_custom_email_class'); function add_custom_email_class($email_classes) { require_once(get_stylesheet_directory() . '/woocommerce/emails/custom-payment-reminder.php'); // Add your custom email class $email_classes['WC_Custom_Payment_Reminder_Email'] = new WC_Custom_Payment_Reminder_Email(); return $email_classes; } And there you go, this works just fine. If I check at woocommerce -> settings -> email I can find the template, and when I click on it I can configure it and at the bottom under "html template" the path to the html template is shown. Now comes the problem: I created a folder in the plugin folder, and created a new file containing the lines from the functions.php (see above). I moved the custom-payment-reminder.php file to the includes folder with that plugin folder and changed the path to the html template file to: $this->template_html = get_stylesheet_directory() . '/woocommerce/emails/custom-payment-reminder-html.php'; After activating the plugin the mail again show fine under woocommerce settings, but when clicking on it, at the bottom under "html template" it says "file not found". I tried changing the path to the html template file, but still the template file can't be found for some reason. Anyone got a clue where to look for the error? Thanks a lot in advance! Update: If from the plugin, I load the file with the email class from the child theme directory, it works! Now the question is why? I is probably something about the path to the html template, but I can't figure out what the problem is :-( It probably needs to be specified relative to the file calling it? Moving functionality from the functions.php to a separate plugin. Accessing files does not work anymore