How to get Caddy, React, and Express to play nice with each other?

Question

So essentially I have a bare minimal application that uses Caddy for reverse proxying, React JS as a frontend, and a Node / Express backend that I would like to deploy to Railway. I am using Dockerfiles for each service as this is a requirement for a future project.

The current issue I am running into is probably a noob-level question but I am getting a: `CORS header ‘Access-Control-Allow-Origin’ missing`  error.  I did make sure to add cors in the `server.js` file:

```js
app.use(cors())
```

Also, an aside, I made sure to run this code as per the common errors documentation page for Railway:
```js
app.listen(port, "0.0.0.0", () =>
{
    console.log(`listening on port ${port}`)
})
```
Here is the project link:
[invite](https://railway.app/invite/NBeMdkV85oM)