LinkedIn API 403 - “访问发布的内容被拒绝”

I'm developing a PHP function to automatically share new articles on Linkedin's user feed, on my company's framework. Authentication works, so tokens are working (I can get my first and last name from LinkedIn at the time of sharing), but I keep getting a 403 error "Access to posting shares denied" in the POST result when sharing an article.

In my app's parameters "r_basicprofile" and "w_share" are checked. But I re-add these scope parameters when I create the authorization URL (I'm using linkedin-php by splashmedia to connect). I'm also connected as an user with both admin and developer privileges on my LinkedIn app. But I still cannot share an article on my own feed.

Here is the part of my code that fails. I'm in AJAX so if I console.log the generated URL, it is valid but returns the 403 error message in JSON format.

/* Create API request to share an article */

//Building up the URL
$url = 'https://api.linkedin.com/v1/people/~/shares?&oauth2_access_token='.$_SESSION['linkedInCreds']['access_token'].'&format=json&message='.rawurlencode($_REQUEST['message']).'&visibility[code]='.$_REQUEST['visibility']['code'];
    $options = array(
        'http' => array(
            'header'  => "Content-type: application/x-www-form-urlencoded
",
            'method'  => 'POST',
            'content' => http_build_query($url)
        )
    );


$context = stream_context_create($options);
$result = file_get_contents($url, false, $context); /***** FAILS: Returns JSON with 403 error code from LinkedIn. *****/

/* Check if $result is true or false and echoes the result. End of AJAX. */

I'm currently stuck with this issue. Apparently this feature wasn't removed by LinkedIn but I can't make it work, could anyone help ?

Thanks in advance.