Create node by post Api call fail with message "Could not determine entity type bundle: \\u0022type\\u0022 field is missing."}

I'm trying to create a node via Drupal API but I get this error:

Got error 'PHP message: PHP Fatal error:  Uncaught GuzzleHttp\\Exception\\ClientException: Client error: `POST https://site.it/entity/node?_format=hal_json` resulted in a `422 Unprocessable Entity` response:\n{"message":"Could not determine entity type bundle: \\u0022type\\u0022 field is missing."}

This is my function:

public function createFaq($notes, $telegram_id){
  $url = "/entity/node?_format=hal_json"; 
  $opt = [
    'headers' => self::$baseHeader,
    'body' => json_encode([
      [
        'type' => [ ['target_id' => 'faq'] ],
        'title' => 'title', 
        'utente' => [ [ 'target_id' => '123462' ] ],
        'field_domanda' => [ [ 'value' => $notes['domanda'] ] ],
        'field_presenza' => [ [ 'value' => $notes['presenza'] == "Si"? true : false ] ],
      ]
    ])
  ];

  $response = $this->client->request('POST', $url , $opt);
  $r = json_decode( $response->getBody());
  return $r; 
}

But it's really strange, because this other function is working:

public static function createUser($title){
  $url= "/entity/node?_format=hal_json"; 
  $opt = [
    'headers' => self::$baseHeader,
    'body' => json_encode([
      'title' => [ [ 'value' => $title ] ],
      'type' => [ [ 'target_id' => 'article' ] ],
    ])
  ];

  $response = $this->client->request('POST', $url , $opt);
  $r = json_decode( $response->getBody());
  return $r; 
}

Can someone understood my error?

This is the code I used to create a node using rest api:

Endpoint: /node?_format=hal_json

Method: POST

Body:

{
  "title": [
    {
      "value": "This is a question"
    }
  ],
  "field_question": [
    {
      "value": "This is the question"
    }
  ],
  "field_options": [
    {
      "value": "This is the right option"
    },
    {
      "value": "This is not the right option"
    },
    {
      "value": "This is defenitely not the right option"
    },
    {
      "value": "This is the most silly option"
    }
  ],
  "type": [
    {
      "target_id": "question"
    }
  ]
}

Enable the Rest UI module to check if the endpoint exists. Actually I can't find the plugin proposing this endpoint but having Rest UI enabled I saw this URI for posting content types.