Message subscribe module don't send emails

Question

I'm working on a project where I have to notify users when a new node is published or a new comment is created. To achieve this, I've installed the Message subscribe module.

I've configured few flags that seem to work: Users can subscribe to new nodes; when I create a new node, I can flag it.

I've also configured messages, but when I create a new node, no email is sent to users.

I've taken a look at Message Subscribe Module (tje module documentation) and I've found few hooks to make it work. I tried them, but they didn't help: No email is sent.

function mymodule_notification_node_presave(\Drupal\Core\Entity\EntityInterface $node) {
  // Get node where comment was posted.
//   $node = $comment->get('entity_id')->first()->get('entity')->getTarget()->getValue();
  // Call message notify service.
  if($node->isPublished()){   //uncomment if need to send only when node published.
  $notifier = \Drupal::service('message_notify.sender');
  // Create a message with node author as message creator.
  $message = Message::create(['template' => 'node_notification', 'uid' => $node->getOwnerId()]);
  $message->set('field_text_message', 'text message');

  $message->save();
  // Send message to message creator(in this case = node author).
  $notifier->send($message);
  } //isPublished if close
}

/*
 * Implements hook_node_insert().
 */
function mymodule_notification_node_insert($node) {
  $message = message_create('node_notification', array('uid' => $node->uid));

  $wrapper = entity_metadata_wrapper('message', $message);
  $wrapper->field_node_ref->set($node);
  //$wrapper->save();  <-  don't need - message_notify_send_message does this

  $notifier = \Drupal::service('message_notify.sender');
  $notifier->send($message);
}

/**
 * Implements hook_node_update().
 */
function mymodule_notification_node_update(Node $node) {
  $message = Message::create([
    'template' => 'update_node',
    'uid' => $node->getOwnerId(),
  ]);
  $message->set('field_node_reference', $node);
  $message->set('field_published', $node->isPublished());
  $message->save();
  $subscribers = \Drupal::service('message_subscribe.subscribers');
  $subscribers->sendMessage($node, $message);
}

Do you have any idea about what I can do wrong?

I have also seen How to use Message Subscribe module? but it didn't help me.