Google contacts - how do I add in custom details via code?

Question

Hi guys I'm trying to interact with google contacts. I can add new contacts to the address book but when it comes to adding details which are custom in nature like lets say 'sport' I'm trying to use the extendedProperty type but its not working .. check my code

$elem = $doc->createElement('gd:extendedProperty');
$elem->setAttribute('name', 'sport');
$elem->setAttribute('value', 'rugby');
$entry->appendChild($elem);

I'm using the code from this tutorial here - I can attach emails to a contact but nothing else. Whats the problem?