Name not being sent to Mailchimp after submit

Hello,

For some reason the Name field in mailchimp top bar is not being sent to the Mailchimp list. The email field gets captured and sent correctly but when I look on the list the name field is empty.

I’ve added this code for the name field to appear

add_action( 'mctb_before_email_field', function() {
    echo '<input type="text" name="NAME" placeholder="Your name" />';
});

add_filter( 'mctb_merge_vars', function( $vars ) {
    $vars['NAME'] = ( isset( $_POST['NAME'] ) ) ? sanitize_text_field( $_POST['NAME'] ) : '';
    return $vars;
});

How can I fix this ?

Thanks

WordPress 4.4.1 , Mailchimp Top Bar 1.2.7, Mailchimp 3.1.1

https://wordpress.org/plugins/mailchimp-top-bar/