I´m trying to run the code below using React to fetch a simple list of orders:
If you already are providing the Authorization: Basic credentials then I don't think you need to also provide them in the URL. You are getting a complaint about that in the error code. Try leaving those out of the URL.
Here is a link with some other examples --> https://shopify.dev/tutorials/build-a-shopify-app-with-node-and-react/embed-your-app-in-shopify. Hope this helps!