Send Drupal Email with the AhaSend Module

<?php
$plugin = \Drupal::service('plugin.manager.mail')->createInstance('ahasend_mail');
$message = [
    'from' => \Drupal::config('system.site')->get('mail'),
    'to' => 'recipient@example.com', 'subject' => 'Drupal sandbox test',
    'body' => ['Hello from AhaSend'], 'headers' => [], 'params' => [], 'langcode' => 'en',
];
if (!$plugin->mail($plugin->format($message))) {
    throw new RuntimeException('Email was not accepted; check the Drupal log.');
}
echo "Accepted by the API; check the AhaSend sandbox log.\n";