csrfmiddelware 에러 질문입니다

Undefined property: stdClass::$csrfToken in /Users/ywkim/StudyPHP/php_blog/app/Middlewares/CsrfTokenMiddleware.php:12
Stack trace:
#0 /Users/ywkim/StudyPHP/php_blog/app/Middlewares/CsrfTokenMiddleware.php(12): App\Providers\ErrorServiceProvider::App\Providers\{closure}(8, 'Undefined prope...', '/Users/ywkim/St...', 12, Array)
#1 /Users/ywkim/StudyPHP/php_blog/vendor/heracles8562/eclair/src/Routing/RequestContext.php(82): App\Middlewares\CsrfTokenMiddleware::process()
#2 /Users/ywkim/StudyPHP/php_blog/vendor/heracles8562/eclair/src/Routing/Route.php(36): Eclair\Routing\RequestContext->runMiddlewares()
#3 /Users/ywkim/StudyPHP/php_blog/app/Providers/RouteServiceProvider.php(17): Eclair\Routing\Route::run()
#4 /Users/ywkim/StudyPHP/php_blog/vendor/heracles8562/eclair/src/Application.php(32): App\Providers\RouteServiceProvider::boot()
#5 [internal function]: Eclair\Application->Eclair\{closure}('App\\Providers\\R...', 4)
#6 /Users/ywkim/StudyPHP/php_blog/vendor/heracles8562/eclair/src/Application.php(32): array_walk(Array, Object(Closure))
#7 /Users/ywkim/StudyPHP/php_blog/public/index.php(7): Eclair\Application->boot()
#8 {main}

<script>
    const $delete = document.getElementById('delete')
    $delete.addEventListener('click', () => {
    alert('/posts/' + '<?=$post->id?>');
        fetch('/posts/' + '<?=$post->id?>', {
            method: 'delete',
            body: JSON.stringify({ _csrfToken: '<?=$_SESSION['CSRF_TOKEN']?>' })
        }).then(() => {
            window.location = '/'
        })
    })
</script>

//delete post
Route::add('delete', '/posts/{id}', '\App\Controllers\PostController::destroy', [
   AuthMiddleware::class,
   RequireMiddleware::class,
   CsrfTokenMiddleware::class
]);

script부분도 강사님꺼 복붙해서 똑같은데 라우터에CsrftokenMiddleware::class 만 추가하면 에러가 납니다.

csrf 미들웨어 들어가있는 다른 라우터는 문제가 안되는데 delete할 때만 저렇게 에러가 나고 삭제처리가 안되네요..

왜그런지 알 수 있을까요

$csrfToken = filter_input(INPUT_POST, '_csrfToken', FILTER_SANITIZE_STRING) ?: json_decode(file_get_contents('php://input'))->_csrfToken;

json_decode(file_get_contents('php://input'))->_csrfToken;