How to clone a roughmix in Api v3?

I'm trying to create a new clone of a roughmix everytime the editor is opened.

Using this:
$new_mix = $client->mixing->cloneAction(KALTURA_MIX_ENTRY_ID);

I get this error on the browser when trying to load the page:
Fatal error: Uncaught exception 'KalturaException' with message 'Missing KS. Session not established' in /var/www/.../kaltura_client_v3/KalturaClientBase.php:307 Stack trace: #0 /var/www/.../kaltura_client_v3/KalturaClient.php(3522): KalturaClientBase->throwExceptionIfError(Array) #1 /var/www/.../index.php(42): KalturaMixingService->cloneAction('0_hwjjggui') #2 {main} thrown in /var/www/.../kaltura_client_v3/KalturaClientBase.php on line 307

I have tried adding this before that code, but no help:
$ks = $client->session->start(KALTURA_PARTNER_ADMIN_SERVICE_SECRET, PARTNER_USER_ID, KalturaSessionType::ADMIN, KALTURA_PARTNER_ID, 86400, "edit:*");

I might be totally on the wrong track here. Not very familiar with this.
I would really appreciate, if someone could help with this quickly.

Thanks in advance!