Updating additional profile fields

[Ted S]

I have created two custom profile fields which the user can not see but are updated based on their other profile data. However, I can't get the update to actually do anything.

This is a plugin at hook location profile_updateprofile

$zipcode = $userdata->fetch_field('field16');

if(isset($zipcode)){
	
 // this is where the code doesn't do anything...
 $userfields = array( 
  'field16' => 'hello',
  'field17' => 'world'
 );
 $userdata->set_userfields($userfields, true, 'admin');

 die("updated");

}

fields16 and 17 are my custom fields. They are hidden fields. I've tried this with and without the set_userfields but to no avail.

Ideas?