message-example.php

<?php

/**
 * Implements hook_node_insert().
 */
function example_node_insert(\Drupal\node\NodeInterface $node) {
  $message = Message::create(['template' => 'node_created']);

  $arguments = [
    '@url' => $node->toUrl()->setAbsolute()->toString(),
  ];

  $message
    ->set('field_node', $node)
    ->setOwner($node->getOwner())
    ->setArguments($arguments);

  // Send via message notify, which will also save it.
  /** @var \Drupal\message_notify\MessageNotifier $message_notifier */
  $message_notifier = \Drupal::service('message_notify.sender');
  $message_notifier->send($message);
}