Access Denied Flash Message

AccessDeniedHandler.php

<?php
namespace AppBundle\Security;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\Security\Core\Exception\AccessDeniedException;
use Symfony\Component\Security\Http\Authorization\AccessDeniedHandlerInterface;
use Symfony\Component\Routing\RouterInterface;

class AccessDeniedHandler implements AccessDeniedHandlerInterface
{
    private $router;
    
    public function __construct(RouterInterface $router)
    {
        $this->router = $router;
    }
  
    public function handle(Request $request, AccessDeniedException $accessDeniedException)
    {
        $request->getSession()->getFlashbag()->add('error', 'Error 403!...');

        $url = $this->router->generate('homepage');
        
        return new RedirectResponse($url);
    }
}

services.yml

services:
    # ...
    app.security.access_denied_handler:
        class: AppBundle\Security\AccessDeniedHandler
        autowire: true

I made the mistake of adding the flash message inside of the voter classes, which caused flash messages to occur in some cases when I didn't want them to. However, I'd like to be able to pass a message as to why the user was denied to the access denied handler. Any suggestion about how best to do that?