**I understand there are many similar questions.** However, I'm still new to MERN and I am looking for a simplified answer to this problem.

I'm following a tutorial on the **MERN** stack, the application is a simple expense calculator and all the functionality worked great until we moved on to adding Express and Mongoose. Here's the server.js file so you can see my mess:

```
const path = require('path');
const express = require('express');
const dotenv = require('dotenv');
const colors = require('colors');
const morgan = require('morgan');
const transactions = require('./routes/transactions');
const connectDB = require('./config/db');

dotenv.config({ path: './config/config.env' });

connectDB();

const app = express();

app.use(express.json());

if(process.env.NODE_ENV === 'development') {
    app.use(morgan('dev'));
}

app.use('api/v1/transactions', transactions);

if(process.env.NODE_ENV === 'production') {
    app.use(express.static('client/build'));

    app.get('*', (req, res) => res.sendFile(path.resolve(__dirname, 'client', 'build', 'index.html')));
}

const PORT = process.env.PORT || 5000;

app.listen(PORT, console.log(`Server running in ${process.env.NODE_ENV} mode on port ${PORT}`));

```

I'm importing everything correctly in package.json so there's probably no need to spam the chat with that. I'm connected to Mongodb, though I'm sure that doesn't make a difference. Anyways, when I use the command to start it, (npm run start), the server goes up on localhost:5000 and I immediately see **Cannot GET /** on the html page.
In the console on Firefox I get the error:

```
Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”). injectGlobalHook.js:513:49

```

On Chrome it says:

```
... it violates the following Content Security Policy directive: "default-src 'none'". Note that 'img-src' was not explicitly set, so 'default-src' is used as a fallback.

```

Also in my terminal it shows **GET / 404 2.201 ms - 139**, but only when I refresh the page. So I know that the error has to do with CSP, and it's in a file I shouldn't touch and haven't touched, but I don't know how to fix it. I've had the error before, but I think I just gave up on that project. An answer would be nice, but an explanation as to why I'm getting this error would be better. Thanks!