I moved my code base from one server to another - no code change, the only difference being https. I modified my app in Soundcloud developers to be https://url
It's hard to debug this exception without seeing the source code. But my guess is that your problem might be related to this issue:
https://github.com/mptre/php-soundcloud/issues/3
Which means that you should modify your accessToken
call and include the extra cURL parameters.
$accessToken = $soundcloud->accessToken($code, $postData, array(
CURLOPT_SSL_VERIFYPEER => false,
CURLOPT_SSL_VERIFYHOST => false,
));