array_merge() error on Stripe checkout process

Hey there,

Just integrating Stripe payments, and getting the following two errors after perch_shop_checkout() is called.

Warning: array_merge(): Argument #1 is not an array in /Users/Gaz/Sites/dev/shop/perch/addons/apps/perch_shop/lib/PerchShop_Base.class.php on line 80

Warning: Cannot modify header information - headers already sent by (output started at /Users/Gaz/Sites/dev/shop/perch/addons/apps/perch_shop/lib/PerchShop_Base.class.php:80) in /Users/Gaz/Sites/dev/shop/perch/core/lib/PerchUtil.class.php on line 194

Here is my checkout code, which is nothing complicated yet:

<?php

if (perch_member_logged_in() && perch_post('stripeToken')) {

    // your 'success' and 'failure' URLs
    $return_url = '/shop/payment/stripe';
    $cancel_url = '/shop/payment/error';

    perch_shop_checkout('stripe', [
        'return_url' => $return_url,
        'cancel_url' => $cancel_url,
        'token'      => perch_post('stripeToken')
    ]);
} else {
    perch_layout('global/header');

  perch_shop_payment_form('stripe');

    perch_layout('global/footer');
}

Any idea what could be causing this?

Diagnostic report:

Perch Runway: 2.8.29, PHP: 5.6.10, MySQL: mysqlnd 5.0.11-dev - 20120503 - $Id: 3c688b6bbc30d36af3ac34fdd4b7b5b787fe5555 $, with PDO
Server OS: Darwin, apache2handler
Installed apps: content (2.8.29), assets (2.8.29), categories (2.8.29), perch_shop_orders (1.0.3), perch_shop_products (1.0.3), perch_shop (1.0.3), perch_members (1.5)
App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_members', 'perch_shop' );
PERCH_LOGINPATH: /perch
PERCH_PATH: /Users/Gaz/Sites/dev/shop/perch
PERCH_CORE: /Users/Gaz/Sites/dev/shop/perch/core
PERCH_RESFILEPATH: /Users/Gaz/Sites/dev/shop/perch/resources
Image manipulation: GD
PHP limits: Max upload 32M, Max POST 32M, Memory: 128M, Total max file upload: 32M
F1: 2edba60ed1f613d6dd804feb202456a2
Resource folder writeable: No
HTTP_HOST: shop.dev.local
DOCUMENT_ROOT: /Users/Gaz/Sites/dev/shop
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php

Thanks!