Perch shop setup issues

Hi - I've recently updated a site from Perch v2.7.4 to Perch v3.0.10, following the instructions as per https://docs.grabaperch.com/perch/upgrading/

The site previously ran Perch Shop Paypal, however this is now removed and the replacement Perch Shop addon has now been installed.

I'm now attaempting to go through the setup for the new addon, but am encountering issues.

When attempting to enter any data such as a new currency, or new country - once I submit the form a blank page is returned. I can't seem to enter any new settings.

Perch: 3.0.10, PHP: 7.0.21, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: b5c5906d452ec590732a93b051f3827e02749b83 $, with PDO
Server OS: Linux, apache2handler
Installed apps: content (3.0.10), assets (3.0.10), categories (3.0.10), perch_blog (5.6.1), perch_shop_orders (1.2.5), perch_shop_products (1.2.5), perch_shop (1.2.5), perch_members (1.6.2)
App runtimes: <?php $apps_list = [ 'perch_blog', 'perch_members', 'perch_shop', ];
PERCH_LOGINPATH: /perch
PERCH_PATH: /var/www/html/perch
PERCH_CORE: /var/www/html/perch/core
PERCH_RESFILEPATH: /var/www/html/perch/resources
Image manipulation:
PHP limits: Max upload 20M, Max POST 20M, Memory: 128M, Total max file upload: 20M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes
HTTP_HOST: rockymountainpizza.com
DOCUMENT_ROOT: /var/www/html
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php

Help appreciated.

T Denty