How to upload photo to page with Graph Api v2.2 - php

Question

I used to create several apps before, but now with the v4 I can't make a simple photo upload to work :( I tried with the 'url' and with the 'source' parameter as well, but nothing works. I want to upload a photo to my own Facebook Page with some caption. I got the access token, the Access Token Debugger says, that it never expires and it has public_profile, read_stream, read_insights, manage_pages, publish_actions, user_photos permissions.
This my code right now:
$accessToken = "MY-ACCESS-TOKEN";
$session = new FacebookSession($accessToken);
$myfile = "file.png"; //created and saved via PHP GD functions
if ( isset( $session ) ) {
try {
$message = "This is my message";
$request = new FacebookRequest(
$session,
'POST',
'/'.$pageid.'/photos',
array (
'source' => realpath("/path/to/" . $myfile),
'message' => $message,
)
);
} catch (FacebookRequestException $e) {
echo "Exception occured, code: " . $e->getCode();
echo " with message: " . $e->getMessage();
} catch (\Exception $e) {
echo "Exception occured, code: " . $e->getCode();
echo " with message: " . $e->getMessage();
}
$response = $request->execute();
$graphObject = $response->getGraphObject();
/* handle the result */
} else {
// show login url
echo 'Login';
}
Right now I get this error:
mod_fcgid: stderr: PHP Fatal error: Uncaught exception 'Facebook\\FacebookAuthorizationException' with message '(#324) Requires upload file' in /data/domains/
What am I doing wrong? Can someone help me, please?
Thank you very much!