How to add Guest Contact to a Meeting via the API

Hi

Does anyone have an example of how to add a Guest Contact to a Meeting via an API call? I have tired the below but still not working.

'contact_name' => $contact_name,
'contact_id' => $contact_id,
  'contacts' => array(array('name'=>$contact_name,'id'=>$contact_id)),
                            'contacts' => array('name'=>$contact_name,'id'=>$contact_id),

This is using the rest-php-client. All other fields set during creation like name and description and the flexi relate account. I am running version 8.1