Update a Custom Field

I was actually able to figure this out. Not sure if it is “technically” the correct way, but it does work.

$contact_service = new Infusionsoft_ContactService();

//this will return the same $contact_id that was sent on success and a 0 (or error out) on failure.
$contact = $contact_service->update( $contact_id, array('_FieldName' => $new_value) );