WordPress: How to return custom REST API response without quotes?

Question

Suppose the following simple custom WP REST API endpoint:

add_action('rest_api_init', function () {
    $namespace = 'wp/v2';

    $routes = ['products', 'product-categories'];
    foreach($routes as $route) {
        register_rest_route($namespace, $route, [
            'methods'   => WP_REST_Server::READABLE,
            'callback'  => 'custom_rest'
        ]);
    }
});

function custom_rest() {
    return new WP_REST_Response('[{}]', 200);
}

How to return the response in the function custom_rest() without single (or double) quotes so that the client can fetch the result as [{}] instead of '[{}]' or "[{}]" ? Like the API returns in the case of /posts

Answer 1

I've just found the answer here https://wordpress.stackexchange.com/a/246261

function custom_rest() {
    header("Content-Type: application/json");
    echo json_encode([]);
    exit();
}