LMR :: Mailchimp for WordPress

map_first_and_last_name.php

<?php
// Use this code to send proper First & Last name to the Mailchimp
// COPY AFTER
add_filter( 'mc4wp_integration_data', function( $data ) {

		if( ! empty( $_POST[ 'first-name' ] ) ) {
			$data[ 'FNAME' ] = sanitize_text_field( $_POST[ 'first_name-6133' ] );
		}
				if( ! empty( $_POST[ 'last-name' ] ) ) {
			$data[ 'LNAME' ] = sanitize_text_field( $_POST[ 'last_name-6133' ] );
		}
	return $data;
});

MC4WP.html

<!-- Mailchimp for WordPress - https://www.mc4wp.com/ -->
<input type="hidden" name="_mc4wp_subscribe_wp-registration-form" value="0">
<p class=" mc4wp-checkbox mc4wp-checkbox-wp-registration-form">
  <label>
    <input type="checkbox" name="_mc4wp_subscribe_wp-registration-form" value="1">
    <span>Yes, add me to your mailing list</span>
  </label>
</p>
<!-- / Mailchimp for WordPress -->
<style>
.lrm-integrations.lrm-integrations--register:not(.lrm-info--register) { display:none; }
</style>