Just can’t get beyond 102 error

I thought integrating the ‘WooCommerce 2Checkout Gateway Payment Free’ (ver2.3) wouldn’t be a big problem but I’m stuck. Using WooCommerce ver3.4.7

Going for the simple implementation:
‘Demo Settings’ set to ‘Parameter’
On the 2checkout account->Site Management I’ve set the following
Currency is euro
‘Direct Return’ is set to ‘Header Redirect (Your URL)’
‘Approved URL’ is set to ‘https://sensorybeanbags.com/?wc-api=WC_Gateway_NM_TwoCheckout’
‘Secret Word’ is set to: There is a value in there which I then copied to the WooCommerce Settings-> payments page.

WooCommerce->Settings->Payments
2checkout enabled. Then under ‘Manage’
Enable – Checked
2CO Account# – as per my customer ID from 2Checkout
‘Secret Word’ – Pasted from the value in 2Checkout->Account->Site Management
‘Enable Demo Mode’ – checked
‘Payment Method’ set to ‘CC’

So much for the settings.
At the checkout, my email address is [email protected]
Phone Number is 203919191

When I select 2checkout and ‘Place Order’, it goes to sandbox, loads the ‘Secure Checkout’ page, and when loading the ‘Review Cart’ segment, no items are displayed, instead I get:
‘An error has occurred during checkout ……ERROR CODE: PE102

Anyone got any idea what I’m doing wrong?

Oliver