CORS issues between two services

Question

I am having trouble getting around CORS issues between my frontend and backend.

My frontend has a public railway domain that I am allowing in my backend
```ts
cors({
  origin: [env.AGORA_URL],
  methods: ["GET", "POST", "PUT", "DELETE"],
}),
...
```

In my frontend I am using my backend's internal url as an env var
```VITE_MERCURY_URL=mercury.railway.internal:8080```

And in my backend i'm doing something similar
```AGORA_URL=https://agora-development.up.railway.app:8080```

Is this the correct way to set it up? Or does the backend also need a public url?

I've tried changing the ports and also removing them but it does not seem to work