Simple REACT app not finding index.html

Was following the tutorial at https://developers.cloudflare.com/workers/tutorials/deploy-a-react-app/ to get a simple REACT app on to a worker. Works aboslutely fine in preview mode but not when published.

On the published worker I get the following error:-
could not find react/index.html in your content namespace

Is this an error in something I am doing or something missing from the demo?