The “Customer invoice / Order details” WooCommerce email notification is often used for manually sending payment requests to customers – it’s not automatically triggered like other WooCommerce emails. You can access it from the individual order screen under the “Order Actions” section.
In certain cases, however, you’d want to make it automatic. And I don’t know why it’s not like that by default. So, let’s fix it: if you create a manual order from the backend, set it as pending, add some products to it and “Save”, the email notification will trigger on its own thanks to the snippet below. Enjoy!
Continue reading WooCommerce: Send Pending Order Email Automatically