I was making my own api in javascript using node and express for flutter, but when I try to send the required body to my api I am getting error that there is no data that is required. this is my api code: index.js(main file):

const express = require('express');
const authRouter = require('./routes/auth');
const PORT = 3000;
const app = express();
app.use(express.json());
app.use(authRouter);
app.get('/', (req, res) => {
    res.send("hello world");
})

app.listen(PORT, '0.0.0.0', () => {
    console.log(`connected at port ${PORT}`)
});

routes/auth file:

const express = require("express");
const authRouter = express.Router();

authRouter.post("/fetchedData", async (req, res)=>{
    try {
        const {sampleName,samplepara} = req.body;
    


        res.status(200).json({sampleName,samplepara});  
        console.log("data received");      
        console.log(sampleName + " "  + samplepara)
        // res.send(sampleName, samplepara)
            
    }
    catch (e) {
        res.status(500).json({ error: e.message })
        console.log(e)
    }
});

// signin Route

module.exports = authRouter;

sending data from flutter code:

 var samples = {
      'sampleName' : 'Ammar',
      'samplepara' : 'this is the para'
    };
    var jf = jsonEncode(samples);
    var url = Uri.parse('http://myIPaddress:3000/fetchedData');
    var response = await http.post(url,
        body: jf,);
    print('Response status: ${response.statusCode}');
    print('Response body: ${response.body}');

but when I try to make a request from vs code extension thunder client so it is working