Facebook数据删除请求JSON响应不符合预期问题求助

我在实现Facebook数据删除请求功能时，Facebook端调用我的回调方法后反馈，我返回的JSON响应不符合其预期。根据Facebook官方文档，要求的响应格式示例为：

{ url: '<url>', confirmation_code: '<code>' }

文档提供的示例代码如下：

$data = array(
  'url' => $status_url,
  'confirmation_code' => $confirmation_code
);
echo json_encode($data);

但这段代码生成的响应和Facebook要求的格式不符——属性名带双引号，值也用双引号包裹。于是我自行构造了响应字符串：

$return_value = "{ url: '$url', confirmation_code: '$confirmation_code' }";

结果仍然失败。我尝试过使用response()->json()、json_encode()方法返回数组或自定义字符串，要么整个字符串被添加双引号，要么URL被转义，这应该就是响应不符合要求的原因。现在想明确：Facebook到底要求该响应的具体格式是什么？

附当前回调方法代码：

public function removeFBDataCallback(Request $request)
{
    $signed_request = $request->get('signed_request');
    $data = $this->parse_signed_request($signed_request);
    $fb_user_id = $data['user_id'];

    $fb_user = $this->UsersRepository->CheckFacebookUIDExisted($fb_user_id);
  
    if (!$fb_user) {
  
        error_log("No user with facebook id: $fb_user_id found when trying to remove data during facebook deletion callback");
        return response()->json(['code' => 403, 'data' => ['message' => 'Facebook user not found when deleting facebook data']]);
    }
    else {
        

        $fb_delete_confirmation = new FBDeleteConfirmation();
        $fb_delete_confirmation->facebook_id = $fb_user->facebook_user_id;
        $fb_delete_confirmation->token = genToken(20);
        $fb_delete_confirmation->save();


        $fb_user->is_account_facebook = 0;
        $fb_user->facebook_user_id = null;
        $fb_user->save();

        
        $confirmation_code = base64_encode("abc123");
        $url = url('login').'/facebook'.'/dataDeleteConfirmation'.'?confirmationid'.('=').($confirmation_code);


        error_log('------------------');

        $return_value = "{ url: '$url', confirmation_code: '$confirmation_code' }";
        error_log($return_value);
        return json_encode($return_value);

    }
    
} 

内容的提问来源于stack exchange，提问作者Esko918