Youtube Data API v3 PHP Account Service: 403 - Forbidden: YoutubeSignupRequired

I've been banging my head about this for 4 hours now so I might need a little help.

What I want to do is store the video on YouTube, for the video contest we have. I really prefer two-legged OAuth access via a service account (I want users even without a gmail account to be able to send videos to us, and I want to put those videos private or unregistered in our YouTube account).

But it doesn't seem to work. My code right now looks something like this:

function go()
{
require_once 'googleClient/Google_Client.php';
require_once 'googleClient/contrib/Google_YoutubeService.php';

define("CLIENT_ID",'xxxxxxx.apps.googleusercontent.com');
define("SERVICE_ACCOUNT_NAME",'xxxxxxx@developer.gserviceaccount.com');
define("KEY_FILE", 'googleClient/verylonghashtagprivacystuff-privatekey.p12');
define("SECRET_FILE", 'client_secrets.json');

$client = new Google_Client();
$client->setApplicationName("My Contest App");

$key = file_get_contents(KEY_FILE);
$secret = file_get_contents(SECRET_FILE);


$GAC = new Google_AssertionCredentials( SERVICE_ACCOUNT_NAME,
array('https://www.googleapis.com/auth/youtube.upload',
            'https://www.googleapis.com/auth/youtube'), 
$key ,'notasecret','http://oauth.net/grant_type/jwt/1.0/bearer');

$client->setAssertionCredentials($GAC);

$client::$auth->refreshTokenWithAssertion();
$client->setClientId(CLIENT_ID); // Did tried to put that one sooner
$client->setClientSecret($secret); // Did tried to put that one sooner
$json = $client->getAccessToken();

$accessToken = json_decode($json)->access_token;
$video = array();
$video["snippet"] = array();


$snippet = new Google_VideoSnippet();
$snippet->setTitle("Contest Video USERNAME");
$snippet->setDescription("Video for contest 2013 USERNAME.");
$snippet->setTags(array("Contest","Whatever","2013"));
$snippet->setCategoryId("22"); //Did tried "Entertainment".

$status = new Google_VideoStatus();
$status->setPrivacyStatus("unlisted");

$video = new Google_Video();
$video->setSnippet($snippet);
$video->setStatus($status);
$client->setAccessToken($json);

$youtube = new Google_YoutubeService($client);
$url = '/projet_video.mp4';

$response = $youtube->videos->insert(
"status,snippet", 
$video, 
array(  'data' => file_get_contents($url),'mimeType' => "video/*")); 
//Did tried video/mp4


return $response ;}

      

        
        
        
      

    

And the result:

error": {  "errors": [   {
    "domain": "youtube.header",
    "reason": "youtubeSignupRequired",
    "message": "Forbidden",
    "locationType": "header",
    "location": "Authorization"
}], "code": 403,  "message": "Forbidden" }