dynamic multi-select from API call

Hello

    what i'm trying to achieve here is to make an API call and use the retrieved values to generate a dynamic multi-select field and be able to save selected options. I have used HOWTO: Have a dropdown field that get's it's options from a function as a start point with no success. This is what i did:

1- created a new dropdown from dropdown editor named test_users_list to attach it to the multi-select field below. The reason i created this list was b/c when you create a multi-select field from studio it can't be empty and i didn't want to use any of the existing ones.

2- created a new multi-select field on campaigns (using dropdown list from step 1) that created the following file

custom/Extension/modules/Campaigns/Ext/Vardefs/sugarfield_test_users_c.php

3- inside that file it contained

<?php
// created: 2017-10-19 03:23:07

$dictionary['Campaign']['fields']['test_users_c']['labelValue']='test users';
$dictionary['Campaign']['fields']['test_users_c']['dependency']='';
$dictionary['Campaign']['fields']['test_users_c']['visibility_grid']='';

?>

4- proceeded to create the function as advised on the HOWTO and my file ended up like this

<?php
// created: 2017-10-19 03:23:07
function getUsers() {
$ch = curl_init('https://jsonplaceholder.typicode.com/users');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($ch);
$userss = json_decode($result, true);

$userList = array();
$userList['']='';
foreach ($userss as $i => $userx) {
$userList[$userss[$i]['username']]=$userss[$i]['name'];
}

return $userList;
}
unset($dictionary['Campaign']['fields']['test_users_c']['options']);
$dictionary['Campaign']['fields']['test_users_c']['function']='getUsers';
$dictionary['Campaign']['fields']['test_users_c']['labelValue']='test users';
$dictionary['Campaign']['fields']['test_users_c']['dependency']='';
$dictionary['Campaign']['fields']['test_users_c']['visibility_grid']='';

?>

Went to campaigns module, edited a campaign and the field is empty the array list wasn't created

One thing that i noticed is that i didn't have 

$dictionary['Campaign']['fields']['test_users_c']['options']

to unset as advised on the HOWTO. I tried removing it with same results.

This HOWTO seems to be for an older version should still work for Ent 7.9.2, what could i be missing?

P.S. the API Call and the Array list do work i tested them separately this is how it looks the array list that should populate the multi-select

Array
(
[] =>
[Bret] => Leanne Graham
[Antonette] => Ervin Howell
[Samantha] => Clementine Bauch
[Karianne] => Patricia Lebsack
[Kamren] => Chelsey Dietrich
[Leopoldo_Corkery] => Mrs. Dennis Schulist
[Elwyn.Skiles] => Kurtis Weissnat
[Maxime_Nienow] => Nicholas Runolfsdottir V
[Delphine] => Glenna Reichert
[Moriah.Stanton] => Clementina DuBuque
)

please advise

Sergio