( ! ) Deprecated: Return type of Slim\Collection::offsetExists($key) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in D:\Wamp\www\PHP\slim3\vendor\slim\slim\Slim\Collection.php on line *112*
Example:
<?php
require 'vendor/autoload.php';
$app = new \Slim\App();
$app->get('/', function (Request $req, Response $res, $args = []) {
return $res->withStatus(200)->write('Hello World');
});