Mongodb – Connection refused by mongo server idk why

I have a mongo model like this:-

var mongoose = require('mongoose');

const itemsModel = new mongoose.Schema({
    _id: {
        type: String,
    },
    userName: {
        type: String,
        required: true
    },
    description: {
        type: String,
        required: false
    },
    itemId: {
        type: String,
        required: true,
        unique: true
    }
});

module.exports = mongoose.model("itemsModel", itemsModel);

and I am handling my backend route in a file called itemRoute.js like this:-

const express = require("express");
const router = express.Router();
const id = require('uuid');
const itemsModel = require("../src/model/itemsModel");

router.post('/add-item/', (req, res) => {
    const { userName, description, itemId } = req.body;

    itemsModel.findOne({
        itemId: itemId,
        userName: userName,
    }, (error, prevData) => {
        if(error){
            return res.send({
                success: false,
                description: `Internal Server Error ${error}`
            });
        }
        
        if (prevData.length > 0){
            itemsModel.findOneAndUpdate(
                { _id: prevData[0]._id }, 
                { description: description },
                (error, status) => {
                    if (error){
                        return res.json({
                            success: false,
                            description: `Internal Server Error ${error}`
                        });
                    } else {
                        return res.status(200).json({
                            success: true,
                            description: "Updated item successfully",
                            prevData: prevData,
                            status: status
                        });
                    }
                }
            );
        }

        const newModel = new itemsModel;
        newModel._id = id.v4();
        newModel.userName = userName;
        newModel.itemId = itemId;
        newModel.description = description;

        newModel.save((error, user) => {
            if(error){
                return res.json({
                    success: false,
                    description: `Internal Server Error ${error}`
                });
            }

            return res.status(200).json({
                success: true,
                description: "Added item to db",
                user: user
            });
        });
    });
});

router.get('/get-items/:itemId/', (req, res) => {
    console.log(req.body);
    const itemId = req.params.itemId;

    return res.status(200).json({
        success: true,
        description: "Nicee",
        id: itemId,
    });
});

module.exports = router;```

I have the following in my index.js express file:-
app.use('/api', require('./routes/itemRoute'));
and I am calling from my frontend like this:-

handleAddItemButton = (event) => {
    event.preventDefault();
    const data = {
      userName: this.props.userName,
      description: this.state.description,
      itemId: this.props.itemId,
    }

    fetch(`http://localhost:8000/api/add-item/`, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify(data)
    })
    .then(res => res.json())
    .then(res => {
      console.log(res);
    })
    .catch((err) => console.log(err));
  };

My index.js file:-

/* jshint esversion:6 */
const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const path = require('path');
const mongoose = require('mongoose');

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
    extended: true
}));
app.use(express.static('./build'));
app.use(express.static('./build/static'));
app.use('/api', require('./routes/auth'));
app.use('/api', require('./routes/items'));
app.use('/api', require('./routes/itemRoute'));
mongoose.set('useCreateIndex', true);

const port = 8000

mongoose.connect('mongodb://localhost:27017/item-app', {
    useNewUrlParser: true
})

app.get('/*', (req, res) => {
    res.sendFile(path.resolve('./build/index.html'))
})

app.listen(port, () => console.log(`server running at ${port}`));

When my frontend actually makes the request, I am thrown the following error:-
POST http://localhost:8000/api/add-item/ net::ERR_CONNECTION_REFUSED
I have looked through my code again and again but to no avail. Any and all help is sincerely appreciated. Please guide me through what Im doing wrong.

Edit 1:-
After @ewokx comment I ran mongod and got the following;-

Is this the issue? How to solve this?