How to send a POST request to Flask API using Fetch in a React app

To demonstrate my problem, I have made a simple example

    import React, { useEffect } from 'react';

    function App() {
  useEffect(() => {
    fetch('/get')
      .then((response) => response.json())
      .then((data) => console.log(data));
  }, []);

  useEffect(() => {
    fetch('/post', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ title: 'React POST Request' })
    })
      .then((response) => response.json())
      .then((data) => console.log(data));
  }, []);

  useEffect(() => {
    fetch('https://jsonplaceholder.typicode.com/posts', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ title: 'React POST Request' })
    })
      .then((response) => response.json())
      .then((data) => console.log(data));
  }, []);

  return <div className="App"></div>;
}

export default App;

In first useEffect hook, I am sending a GET request to my flask API and logging the response of request.

In second useEffect hook, I am sending a POST request to my flask API and logging the response of request.

In thirduseEffect hook, I am sending a POST request to jsonplaceholder.typicode.com/posts and logging the response of request.

first useEffect output:

second useEffect output:

third useEffect output:

I am using the same post request code for request for my Flask API and jsonplaceholder.typicode.com API but response of my API is always empty object {}. Which is not expected. It should return this { title: 'React POST Request' } object. I try to find the solution but nothing work for me.

My simple Flask API:

import time
from flask import Flask, request
from flask_cors import CORS


app = Flask(__name__)
CORS(app)

@app.route('/get', methods=['GET'])
def get():
   return { "title": 'React GET Request' }

@app.route('/post', methods=['POST'])
def post():
   return request.args

.flaskenv file:

FLASK_APP=api.py
FLASK_ENV=development

package.json file:

{
  "name": "flask-app-demo",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@testing-library/jest-dom": "^5.11.8",
    "@testing-library/react": "^11.2.3",
    "@testing-library/user-event": "^12.6.0",
    "react": "^17.0.1",
    "react-dom": "^17.0.1",
    "react-scripts": "4.0.1",
    "web-vitals": "^0.2.4"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },
  "proxy": "http://localhost:5000"
}

By the way, I am using create-react-app package to setup my React App.