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To set up the development environment for our payment app, we need to install the necessary software and tools. Here are the steps:

1. Node.js and npm: Node.js is a JavaScript runtime that allows us to run JavaScript code on the server-side. npm is the package manager for Node.js. Download and install Node.js from the official website: https://nodejs.org/. Make sure to install the LTS version.

2. MongoDB: MongoDB is a NoSQL database that we'll be using as our database for the payment app. Download and install MongoDB from the official website: https://www.mongodb.com/try/download/community.

3. React: React is a JavaScript library for building user interfaces. Install React using the following command in your terminal:

1npx create-react-app payment-app

4. Stripe: Stripe is a popular payment platform that we'll be integrating into our payment app. Install the Stripe library using the following command in your terminal:

1npm install stripe

After installing these software and tools, you are ready to start developing the payment app. Use the following code as a starting point to create a simple Express server:

1// Replace with your desired code
2
3const express = require('express');
4const app = express();
5
6app.get('/', (req, res) => {
7  res.send('Hello, World!');
8});
9
10app.listen(3000, () => {
11  console.log('Server is running on port 3000');
12});

With these steps, you have successfully set up the development environment for our payment app. Next, we will move on to creating the user interface. Stay tuned!