AnnotationException when trying to use type

[angekouf]

I am trying to follow the example in the docs but I get an annotation error.

Example user class

use Ivory\Serializer\Mapping\Annotation as Serializer;

class User
{
	/**
	 * @Serializer\Type("string")
	 *
	 * @var string
	 */
	public $username;
	
	public function __construct(string $username) {
		$this->username = $username;
	}
}

Using serializer to serialize object to json

$obj = new User('testing');
var_dump($obj);

$serializer = new \Ivory\Serializer\Serializer();

$json = $serializer->serialize($obj, \Ivory\Serializer\Format::JSON);

var_dump($json);

It throws following error

AnnotationException in AnnotationException.php line 54: [Semantical Error] The annotation "@ivory\Serializer\Mapping\Annotation\Type" in property User::$username does not exist, or could not be auto-loaded.

What am I doing wrong?

In the end I want to use custom classes instead of string but it is not working even for string