PayPal Checkout actions.payment.get() returns 400 ack: contingency, contingency: PERMISSION_DENIED

[BOSWebMonkey]

Scenario

I have modified the code slightly on the demo checkout ( https://developer.paypal.com/demo/checkout/#/pattern/client )

 onAuthorize: function(data, actions) {
            return actions.payment.execute().then(function() {
                window.alert('Payment Complete!');
            });
        }

Becomes

 onAuthorize: function(data, actions) {
         return actions.payment.execute().then(function() {
                    return actions.payment.get().then(function(persondata){
                        window.alert('Payment Complete '+persondata.payer.payer_info.first_name);
                    });
        });
]

This works as expected on https://developer.paypal.com/demo/checkout/#/pattern/client and the popup prompt appears with the customer name

However, when copying the exact same code from the demo checkout to a page on my own domain, the payment is processed but the actions.payment.get() function returns the following:

Header

Request URL: https://www.paypal.com/webapps/hermes/api/payment/PAYID-LOQTRBA76N61243AL182344V?
Request method: GET
Remote address: 2.20.93.6:443
Status code: 400

Response

{"ack":"contingency","contingency":"PERMISSION_DENIED","meta":{"calc":"5f88aa48560db","rlog":"f5dfmutjx1gQV2oeahemZJyv%2FSY8VvcRRrHSUbQ38ZMf%2BpvEnwj5o40X0QQ0RUwuYQ3YfCadK7MVCKfPsJt9GQ_165edc5cad5"},"server":"_-SZvonM_8Tv7DuwTYyMD160uHjZVXSDqnaTVOe2HemF9Eo36wzxj-tzP55LuZ6VXds73rq8LcK_PffuRdmKb7xD7QQ9RbowLr209sPkHR6HIOMLq-JBlr4HJmHJzid0lK5-M1TmfwoiteQRzoP4GW3YDMlhf8yb4Cdm9wK_YSr-FTbnke8iKwQeBtq7Iuu17p8DdwDMNY2YJqJBQ0QeTWEf_-n9A4XK2ul4EZyEtj1IenatahG7xG"}

Is there some kind of domain based blocking going on here?

[BOSWebMonkey]

One further point

This works ok in Sandbox mode on both environments

It's when I run it in Production mode that the problem occurs