"isAJAX()" method always return false;

I tried to create an API with a script like the one below. when I run it with $.ajax , the application always returns the "false" value in the isAJAX method. Whats wrong?
Thanks before.

PHP Code:

<?php 
namespace App\Controllers\Api;

use function time;
use CodeIgniter\API\ResponseTrait;
use CodeIgniter\Controller;
use CodeIgniter\HTTP\ResponseInterface;

final class Test extends Controller 
{
    use ResponseTrait;

    public function index(): ResponseInterface
    {
        return $this->respond([
            'ack' => time(),
            'req' => $this->request->getPost('foo'),
            'head' => $this->request->getServer('HTTP_BEARER'),
            'ajax' => $this->request->isAJAX(),
            ]);
    }
} 


In my case all works fine.

Header on welcome_message.php

Code:

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js"></script>
        <script>
           jQuery(document).ready(function () {
               $.ajax({
                   url: '/ajax-html',
                   method: 'GET',
                   success: function (data) {
                       console.log(data);
                   }
               })
           })
</script>

Routes.php

PHP Code:

$routes->get('/ajax-html', 'Home::ajaxOrHtml'); 


Controller Home.php

PHP Code:

<?php namespace App\Controllers;

use CodeIgniter\API\ResponseTrait;
use CodeIgniter\Controller;

class Home extends Controller
{
    use ResponseTrait;

    public function ajaxOrHtml () {
        if ($this->request->isAJAX()) {
            return $this->respond([
                'isAjax' => $this->request->isAJAX()
            ]);
        }
        return view('ajax_view');
    }
}