Node JS Type Error : Cannot read property

I am a beginner nodejs developer, and for a start I decided to develop a blog project for practice. I am using Nodejs Express and native js on the client. When adding a post, nodejs throws an error in the routes:
(node: 25967) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'title' of undefined at router.post (/routes/post.js:15:25)
Here is my code:

routes/post.js

const express = require('express');
const router = express.Router();
const Post = require('../models/Post');

// http://localhost:5000/api/post (GET)
router.get('/', async (req, res) => {
    const posts = await Post.find({})
    res.status(200).json(posts)
})

// http://localhost:5000/api/post (POST)
router.post('/', async (req, res) => {

    const postData = {
        title: req.body.title,
        text: req.body.text
    }

    const post = new Post(postData)

    await post.save()
    res.status(201).json(post)
})

// http://localhost:5000/api/post/id (DELETE)
router.delete('/:postId', async (req, res) => {
  await  Post.remove({_id: req.params.PostId})
  res.status(200).json({
      message: 'Deleted'
  })
})




module.exports = router

app.js

const express = require('express');
const path = require('path');
const bodyParser = require('body-parser')
const mongoose = require('mongoose');
const postRouter = require('./routes/post');
const keys = require("./keys");

const port = process.env.PORT || 5000;
const clientPath = path.join(__dirname, 'client');

const app = express();
app.use(express.static(clientPath))
app.use('/api/post', postRouter)
app.use(bodyParser.json())


mongoose.connect(keys.mongoURI, { useNewUrlParser: true, 
    useUnifiedTopology: true, useCreateIndex: true })
    .then(() => console.log('MongoDB connected'))
    .catch( err => console.error(err));



app.listen(port, () => {
    console.log(`Server has been started on port ${port}`);
});

(model)Post.js

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const postSchema = new Schema ({
    title: {
        type: String,
        required: true,
    },
    text: {
        type: String,
        required: true
    },
    date : {
        type: Date,
        default: Date.now
    }
})

module.exports = mongoose.model('posts', postSchema)

what could be the problem?