Mongo DB not connecting to NodeJS after Heroku deployment - node.js

Question

I've a MERN app (Mongo Express React Node) that works locally, and connects to my MongoDB database, getting data.
The React front-end works after I deploy it to Heroku, but Nodejs won't connect to MongoDB on Heroku.
The environment variables like MONGO_URI stored as Heroku config variables, works perfectly fine, yet it just won't connect to my MongoDB.
The Heroku logs shows the error message: DISCONNECTED FROM MONGO DB from my server.js file.
How can I solve this?
server.js file
const express = require("express");
const dotenv = require("dotenv");
const cookieParser = require("cookie-parser");
const mongoose = require("mongoose");
const cors = require("cors");
const path = require("path");
dotenv.config();
const authRouter = require("./routes/auth");
const blogRouter = require("./routes/blog");
const userRouter = require("./routes/user");
const app = express();
app.use(express.json());
app.use(cookieParser());
app.use(cors());
app.use("/api/auth", authRouter);
app.use("/api/user", userRouter);
app.use("/api/blog", blogRouter);
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 connect = () => {
mongoose
.connect(process.env.MONGO_URL,
{useNewUrlParser: true,
useUnifiedTopology: true,
useNewUrlParser: true})
.then(() => {
console.log("CONNECTED TO THE MONGO DB");
})
.catch((err) => {
console.log(err);
mongoose.disconnect(() => {
console.log("DISCONNECTED FROM MONGO DB");
});
})
};
app.listen(process.env.PORT || 8000, () => {
connect();
console.log("MONGO_URL", process.env.MONGO_URL);
console.log("PASSCODE", process.env.PASSCODE);
console.log(`LISTENING ON PORT ${process.env.PORT}`);
})

Answer 1

Your environment variable to connect to MongoDB database has to be MONGO_URI, not MONGO_URL.
Otherwise it won't work.