Post Indexer Custom Query

I am using network_query_posts() to do a custom query of Post Indexer. So far, things have been going as expected, but have run into a couple spots where I cannot pull post info like that on the actual site itself. I had an issue with getting the correct post publish date, but have that figured out now, however, I ran into another issue with getting terms from custom taxonomies.

I have been using the below with success on the individual sites within the loop, however, when I try to query Post Indexer it does not return any values.

$post_main_terms = get_the_terms($postID, 'main-categories');
if (!empty($post_main_terms)){
$post_main_term = array_shift($post_main_terms);
$post_main_cat = $post_main_term->name;
}

I have tried numerous things, including using network_get_the_terms(), etc (too many to put on here), but nothing is returned for the value of the terms. So, would you be able to help me out with what I need to do in order to retrieve values of custom post categories/taxonomies?

Also, is there any documentation on more things like this to be able to pull info from each post Post Indexer indexes using the network_query_posts()?

Also, to make sure I have this setup correctly, this is what I am using for my query:

<?php
$args = array(
'post_type' => 'post',
'category_name' => 'name'
);

network_query_posts($args);
if ( network_have_posts() ) {
while ( network_have_posts() ) {
network_the_post();

// Content here for each post

}

network_reset_postdata();
?>