Why aren’t my keys and values providing the right response on my API testing on Postman?

I am using Postman to test the API that handles form submissions for my web application, but I am getting the wrong response for my firstName and lastName sections. Regardless of what I input in these sections. Even if I leave them empty or just input # value for firstName and @ value for lastName, I keep getting 200 OK Form submitted successfully. However, I want it to send a 400 Bad request if the firstName or lastName is less than two characters each, and includes anything other than letters. For my email and message sections, those are working correctly. I only have problems with firstName and lastName.

This is what I have for my code:

const express = require('express');
const bodyParser = require('body-parser');
const app = express();
const port = 3000;

app.use(bodyParser.urlencoded({ extended: true })); // Use body-parser middleware to parse request     bodies

// Serve static files from the public directory
app.use(express.static('public'));

// Parse incoming form submissions
app.use(express.urlencoded({ extended: true }));

// Handle form submission
app.post(
    '/submit-form',
    [
      body('firstName')
        .isAlpha()
        .isLength({ min: 2 })
        .withMessage('First name must be at least 2 letters and contain only letters.'),
      body('lastName')
        .isAlpha()
        .isLength({ min: 2 })
        .withMessage('Last name must be at least 2 letters and contain only letters.'),
      body('email')
        .isEmail()
        .withMessage('Invalid email format.'),
      body('message')
        .trim()
        .notEmpty()
        .withMessage('Message cannot be empty.'),
    ],
     (req, res) => {
      const errors = validationResult(req);
      if (!errors.isEmpty()) {
        return res.status(400).json({ errors: errors.array() });
      }

      const firstName = req.body.firstName;
      const lastName = req.body.lastName;
      const email = req.body.email;
      const message = req.body.message;

  // Send a response back to the client
  res.status(200).send('Form submitted successfully');
});

// Route to display a confirmation message
app.get('/confirmation', (req, res) => {
    // Code to display confirmation message 
    res.status(200).send('Thank you for submitting the form!');
});

// Start server
app.listen(3000, () => console.log('Server started on port 3000'));