I am trying to add Calls to the CRM using the API 2.0 and PHP

I am retrieving call CDR records from our phone system, and I want to insert them into the Calls module, but with the 'Owner' being the relevent user.

I have tried the following:

1. $user = ZCRMOrganization::getInstance()->getUser($userId);
   
2. 
   
3. //Confirm we have the user object
   
4. print_r($user);
   
5. 
   
6. //Create empty call instance
   
7. $callInstance = ZCRMRecord::getInstance("Calls",null);
   
8. 
   
9. //Other code in here
10. 
    
11. //Set the owner
    $callInstance->setOwner($user);

This returns the error:

zohocrm\php-sdk\src\com\zoho\crm\library\api\handler\EntityAPIHandler.php:232

The same error is returned if I pass the ID as a string, or the e-mail address of the user.

I have also tried

1. $callInstance->setFieldValue("Owner", $user);

Any ideas?

If I remove the owner section - it works fine, but creates the records as "me" - which is how I authenticated throught the API. My user is an Administrator.