模板数据必须是JSON编码的字典错误

I'm trying to post one photo with some text to my Facebook Page, but right now I get this error message:

Template data must be a JSON-encoded dictionary, of the form {'key-1': 'value-1', 'key-2': 'value-2', ...}

This is my code:

<?php 
session_start();

require_once __DIR__ . '/Facebook/autoload.php';

$filename = __DIR__ . '/static/images/test.png';

$acces_token = "my-valid-never-expiring-page-acces-token";

$pageid = "987654321987654321";

echo "<p>START</ps>";

$fb = new Facebook\Facebook([
  'app_id'     => '123456789',
  'app_secret' => 'appsecret123456789abc',
  'default_graph_version' => 'v2.8',
  ]);
    try {
        $response = $fb->post(
            '/'.$pageid.'/feed',
            array(
                "message" => "test test",
                "source" => new CURLFile($filename, 'image/png')
            ),
            $acces_token
        );
    }catch(Facebook\Exceptions\FacebookSDKException $e) {
      echo $e->getMessage();
      exit;
    }
    catch(Facebook\Exceptions\FacebookAuthenticationException $e) {
      echo $e->getMessage();
      exit;
    }

?>

Sadly I don't see any errors on the server in the error.log, so it must be something within the Facebook API :(

What am I doing wrong? Thank you!

EDIT:

After changing '/'.$pageid.'/feed' to '/'.$pageid.'/photos' the problem is gone, but I have another one:

(#324) Requires upload file

I found the solution myself:

$response = $fb->post(
    '/'.$pageid.'/photos',
    array(
        "message" => "test test",
        "source" => $fb->fileToUpload($filename)
    ),
    $tokens[$i]
);