IP-1.5.3 online payments blank screen

I am running IP-1.5.3.

I have enabled online payments and have added PayPal Express and Stripe as payment providers. I have added the correct details for both providers and used live/production API keys for both.

However when I go to the guest URL for an invoice (upaid, of course) and click on the ‘Pay Now’ link, all I get is a blank page.

I can find no errors in chrome developer console and nothing that suggests an error or problem in /application/logs.

Application log:

DEBUG - 2017-08-27 13:21:40 --> UTF-8 Support Enabled
DEBUG - 2017-08-27 13:21:40 --> Global POST, GET and COOKIE data sanitized
DEBUG - 2017-08-27 13:21:40 --> Payment_Handler MX_Controller Initialized
DEBUG - 2017-08-27 13:21:40 --> Config file loaded: /home/rhyshay1/public_html/dev.invoice.pickle-it.co.uk/application/config/invoice_plane.php
DEBUG - 2017-08-27 13:21:40 --> Encryption: Auto-configured driver 'openssl'.
DEBUG - 2017-08-27 13:21:40 --> File loaded: /home/rhyshay1/public_html/dev.invoice.pickle-it.co.uk/application/modules/settings/models/Mdl_settings.php
DEBUG - 2017-08-27 13:21:40 --> File loaded: /home/rhyshay1/public_html/dev.invoice.pickle-it.co.uk/application/controllers/../modules/layout/controllers/Layout.php
DEBUG - 2017-08-27 13:21:40 --> Layout MX_Controller Initialized
DEBUG - 2017-08-27 13:21:40 --> File loaded: /home/rhyshay1/public_html/dev.invoice.pickle-it.co.uk/application/modules/invoices/models/Mdl_invoices.php
DEBUG - 2017-08-27 13:21:40 --> Total execution time: 0.0648

Any ideas ?

Thanks

David