Proxy error? Is there some type of misconfiguration between both hosts?

So I am using proxy in order to share two domains. My issue is that sometimes my HTML will get rendered and will show the whole content of the template in the browser. But when I refresh the page, it acts as if it were the backend host, only rendering bits of information. For example, when I refresh my home page all I get is “res.send(Hello)” instead of the actual HTML and CSS. I followed one method of implementing it, which is this way. My
proxy.config.json

{
    "/":{
        "target": "http://localhost:3000",
        "secure": false,
        "logLevel": "debug"
    }
}

This is my package.json

{
  "name": "mean",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    "start": "ng serve --proxy-config proxy.config.json", // Here
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },

And in my frontend services I am using http://localhost:4200

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