trouble adding custom mail merge fields for MailChimp

I am having trouble adding custom mail merge fields for MailChimp.

The only instructions I have seen to edit s2-hacks.php is “adjust as necessary.”

The s2member Custom Registration/Profile Fields contains a field with a Unique ID of street_address and MailChimp has the field tag of SA, so I thought I should add
‘SA’ => $args->street_address,
to /wp-content/mu-plugins/s2-hacks.php

The log record shows the SA, but no street_address from the registration form. How do I get the street_address to transfer to MailChimp?

[api_merge_array] => Array
(
[MERGE1] => Ian
[MERGE2] => Wright
[OPTIN_IP] => 108.17.132.38
[OPTIN_TIME] => 2015-11-14 13:08:03
[ROLE] => subscriber
[LEVEL] => 0
[CCAPS] =>
[LOGIN] => IanWright
[USER_ID] => 101040
[SA] =>
)

/wp-content/mu-plugins/s2-hacks.php
<?php
add_filter(‘ws_plugin__s2member_mailchimp_merge_array’, function ($custom_fields, $vars)
{
$args = &$vars[‘args’]; // stdClass object.
# print_r($args); // for a full list of all properties.

$custom_fields = array_merge($custom_fields, array(
‘ROLE’ => $args->role,
‘LEVEL’ => $args->level,
‘CCAPS’ => $args->ccaps,
‘LOGIN’ => $args->login,
‘USER_ID’ => $args->user_id,
‘SA’ => $args->street_address,
));
return $custom_fields;

// Note that custom fields (aka: merge tags) will NOT work unless & until they are created by
// a site owner working inside their MailChimp account. They must first add the custom fields
// so they can be filled by the s2Member filter seen here.

// See: <http://kb.mailchimp.com/merge-tags/using/getting-started-with-merge-tags&gt;
}, 10, 2);
add_filter(“ws_plugin__s2member_mailchimp_double_optin”, “__return_false”);

https://wordpress.org/plugins/s2member/