403 Error with destination to NWG service

I've configured a destination in a HCP trial account and I'm getting a 403 Forbidden error.  I'm able to access the service using Postman.

The configuration of the destination is shown below.  I followed the instructions in How to configure an external GW system with SAP Web IDE.

The relevant portion of my index.html file is:

<script>
       var oDataModel = new sap.ui.model.odata.ODataModel("/gbihana/sap/opu/odata/sap/ZOSCI_GBI_HANA_ODATA_1_SRV");
 
 
       var oSalesOrdersList = new sap.m.List({headerText:"All Customers"});
       oSalesOrdersList.setModel(oDataModel);
       oSalesOrdersList.bindItems({
          path: "/Customers",
          template : new sap.m.StandardListItem({
            title: "{CUSTOMER_NAME}"
          })
       });
       oSalesOrdersList.placeAt("content");
    </script>

and my new-app.json file:

 "routes": [
      {
      "path": "/gbihana",
      "target": {
        "type": "destination",
        "name": "HANAGBI"
      },
      "description": "Fiori Trial Demo Backend System"
    },

The error looks like this in Chromes developer tools:

I have successfully configured Open Weather service that Rui described in Lightweight HTML5 apps and Git on SAP HANA Cloud Platform but HCP is pretty new to me and I'm sure I'm missing one small detail but I'm out of ideas.  I've seen the error mentioned in the comments of a couple of blogs but there is never a resolution mentioned.

Any help would be appreciated,

Ross