Error with composer: Uncaught Error: Class 'Firebase \ JWT \ JWT' not found in

I'm trying to login with tokens with the JWT library, I already have the composer installed and I'm guiding myself with the following example:

require_once 'vendor/autoload.php';

    use Firebase\JWT\JWT;

    $time = time();
    $key = 'my_secret_key';

    $token = array(
        'iat' => $time, // Tiempo que inició el token
        'exp' => $time + (60*60), // Tiempo que expirará el token (+1 hora)
        'data' => [ // información del usuario
            'id' => 1,
            'name' => 'Eduardo'
        ]
    );

    $jwt = JWT::encode($token, $key);

    $data = JWT::decode($jwt, $key, array('HS256'));

    var_dump($data);

But I get the following error:

  

Fatal error: Uncaught Error: Class 'Firebase \ JWT \ JWT' not found in   C: \ xampp \ htdocs \ webServiceMGRex \ query.php: 19 Stack trace: # 0 {main}   thrown in C: \ xampp \ htdocs \ webServiceMGRex \ query.php on line 19

I do not know what I'm doing wrong, once you install the composer run this command line

  

composer requires firebase / php-jwt