Temporary fix for WP eCommerce not reporting Payment Method in notification emails. See https://github.com/wp-e-commerce/WP-e-Commerce/issues/2152

wpsc-fix-notification-payment-method.php

<?php
/*
Plugin Name: WP eCommerce Payment Method notifications fix
Plugin URI: https://gist.github.com/webaware/4635d476e506c95c26c66a121631a7dc
Description: temporary fix for WP eCommerce not reporting Payment Method in notification emails
Author: WebAware
Author URI: https://shop.webaware.com.au/
*/

if (!defined('ABSPATH')) {
    exit;
}

add_filter('wpsc_purchase_log_notification_common_args', function($args, $notification) {

    if (empty($args['payment_method'])) {
        $args['payment_method'] = $notification->get_purchase_log()->get('gateway');
    }

    return $args;

}, 10, 2);