Following JustinSainton’s advice, I modified functions.php to fix the issue of file_get_contents being disabled for remote files:
I replaced the line:
$user = json_decode(@file_get_contents('https://graph.facebook.com/me?access_token=' . $cookie['access_token']));
With:
$remote_get = wp_remote_get('https://graph.facebook.com/me?access_token=' . $cookie['access_token']);
$body_content = $remote_get['body'];
$user = json_decode($body_content);
…and this fixed the issue for me.
I’m new to www.ads-software.com and I don’t know if this is the appropriate place to post bug fixes, but I just submitted this out of impulse since I managed the fix the error on my side.