Alright, I've about reached the end of my sanity on this one.

So, I have a basic React frontend w/ an Express backend. React is running off of localhost:3000, the backend is running off of localhost:3030. Following along on a guide for setting up some Spotify integration, everything works fine up until I hit the portion on setting up a proxy. (I have a slightly different setup from the Spotify guide, all my stuff runs through /spotify/auth rather than /auth)

I installed http-proxy-middleware, created the setupProxy.js in my /src folder, and if I ever try to load up localhost:3000 as normal, I get nothing-- my app doesn't load at all.

The only way to have the app appear again is to remove the file. The one on the spotify guide is a bit out of date as far as I can tell anyway, but even using suggestions found elsewhere, I've gotten no luck. Here is the current setup I have for my setupProxy.js file:

const { createProxyMiddleware } = require("http-proxy-middleware");

module.exports = function (app) {
  app.use(
    "/spotify/**",
    createProxyMiddleware({
      target: "http://localhost:3030",
      changeOrigin: true,
    })
  );
};

I've even removed the actual fetch that would be making use of the proxy and still have no luck loading my page. I am also unable to use "proxy": "http://localhost:3030" in my package.json as it throws:

Invalid options object. Dev Server has been initialized using an options object that does not match the API schema.

- options.allowedHosts[0] should be a non-empty string."