Use the env.file Answer

The solution is:

var express = require('express');
var app = express();
require('dotenv').config()

console.log('Hello World');


app.get('/', function(req, res){
    absolutePath = __dirname + "/views/index.html";
    res.sendFile(absolutePath);

});

app.use("/public", express.static(__dirname + "/public"));


app.get('/json', function(req, res){
var data={"message":"Hello json"}
    if (process.env.MESSAGE_STYLE==="uppercase"){
        var data.message=data.message.toUpperCase();
} 
    
    
    res.json(data);

});

module.exports = app;

Your response is missing something. You’re returning a string, the instructions ask for something else.

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).

This ‘link’ won’t work for anyone but you, by the way.

Thanks for notifying.