function my_contacts_list() {

    if( ! function_exists( 'wp_fusion' ) ) {
        return;
    }

    wp_fusion()->crm->connect();

    $return_fields = array( 'Contact.Id', 'Contact.FirstName', 'Contact.LastName', 'Contact.Email' );

    $contacts = wp_fusion()->crm->app->dsQuery( "ContactGroupAssign", 1000, 0, array( 'GroupId' => $tag_id ), $return_fields );

    $out = '<ul>';

    foreach( $contacts as $contact ) {
        $out .= '<li>' . $contact['first_name'] . ' ' . $contact['last_name'] . ' - ' . $contact['user_email'] . '</li>';
    }

    $out .= '</ul>';

    return $out;

}

add_shortcode( 'contacts_list', 'my_contacts_list' );