In my express.js backend (connected to flutter frontend), I have two routes: POST /auth/registrasi and POST /auth/login.
If I run the backend on my localhost, both routes worked (I have tested it using Postman as well).

Strangely, when I deploy my backend to remote server and try to access both routes, POST /auth/login works just fine while POST /auth/registrasi makes my flutter screen show a message saying it can’t do the POST request.

Postman says my POST /auth/login returns 200 OK, while POST /auth/registrasi returns 404 NOT FOUND. But the thing is the /auth/registrasi returns 200 OK as well when I run it on localhost.

Here is my app.js:

import express from 'express';
import bodyParser from 'body-parser';
import cors from 'cors';
import authRoutes from './routes/auth.routes.js'; // Importing routes
// import { dotenv } from 'dotenv';
import { populateDB, getUsernameById, getUserByUserName } from './databases/populate.postgre.js';
import { Sequelize } from 'sequelize';
import http from 'http';
import db from './databases/config.js';
import otpRoutes from './routes/otp.routes.js'; // Importing routes
import UserRoutes from './routes/user.routes.js'; // Importing routes

const app = express();
const PORT = 3001;
// Allow specific origin
const allowedOrigins = [
  'http://localhost:', // Untuk web dari localhost
  'http://http://10.0.2.2:', // Ganti dengan IP komputer host Anda
  'http://http://192',
  'http://http://196',
];
app.use(cors({
  origin: '*',
  methods: ['GET', 'POST'],   // Allowed HTTP methods
  credentials: true           // Allow cookies and credentials
}));
app.use(bodyParser.json()); // Middleware to parse JSON requests
var allowCrossDomain = function(req, res, next) {
  res.header('Access-Control-Allow-Origin', '*');
  res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
  res.header('Access-Control-Allow-Headers', 'Content-Type');

  next();
}
app.use(allowCrossDomain);

app.get('/', (req, res) => {
  res.send('Welcome to the API!');
});
app.use('/auth', authRoutes); // Use authentication routes
app.use('/otp', otpRoutes); // Add OTP routes
app.use('/user', UserRoutes); 
 
app.get('/populate', async (req, res) => {
  await populateDB(); // Call the function to populate the database
  res.send('Database populated!');
});
app.get('/user/:id', async (req, res, next) => {
  const userId = parseInt(req.params.id, 10);
  const [results] = await db.query(`
    SELECT username, email
      FROM users
      WHERE id = ${userId};`);
  // res.send(results[0].username);
  res.send(results);
});
app.get('/username/:username', async (req, res, next) => {
  // const userId = parseInt(req.params.id, 10);
  const [ results ] = await db.query(`SELECT id FROM users WHERE username = '${req.params.username}'`);

  // res.send(results[0].username);
  res.send(results);
});
app.get('/cekOtp', async (req, res, next) => {
  // const userId = parseInt(req.params.id, 10);
  const [ result ] = await db.query(`
    SELECT otp
      FROM users
      WHERE username = 'paksi4' AND email = '[email protected]';
  `);
  const tipe = typeof result[0].otp;
  // res.send(results[0].username);
  res.send(tipe);
});
app.listen(PORT, () => {
  console.log(`Server running on http://localhost:${PORT}`);
}); 

Here is my auth.routes.js:

import dotenv from 'dotenv';  // Load environment variables from the .env file

import { Router } from 'express';
import { compare } from 'bcrypt';
import jwt from 'jsonwebtoken';
import { getUserByUserName } from '../databases/populate.postgre.js';
import db from '../databases/config.js';

dotenv.config();  // Load environment variables
dotenv.config({ path: '.env.development.local' }); // Load environment variables

const { sign, verify } = jwt;
const router = Router();

const users = [
  {
    id: 1,
    username: 'k1',
    email: '[email protected]',
    password: '$2a$12$zPlq1NLDZmgofBpy6LwiB.2q5zSU5TGQdk3Fh3Ll.PFYc7mrQXaAa' // bcrypt hash for 'ti3a'
  }
];

const SECRET_KEY = process.env.JWT_SECRET_KEY;

router.post('/registrasi', async (req, res) => {
  const { username, email, password } = req.body;
    
  if (!username || !email || !password) {
    return res.status(400).json({ error: 'Seluruh isian harus diisi' });
  }
  const [ checkUsername ] = await db.query(`SELECT id FROM users WHERE username = '${username}'`);
    
  if (checkUsername.length > 0) {
    return res.status(400).json({ error: 'Username sudah terdaftar' });
  }
  
  try {
    await db.query(`
      INSERT INTO users (username, email, password, status)
        VALUES ('${username}', '${email}', '${password}','activated');
    `);
    res.status(200).json({ message: 'Registrasi berhasil', berhasil: true});
  } catch (err) {
    res.status(500).json({ error: `Kesalahan:n${err}` });
  }
});
router.post('/login', async (req, res) => {
    const { username, password } = req.body;

    const [ userData ] = await db.query(`SELECT id, username, email, password FROM users WHERE username = "${username}" OR email = "${username}";`);
    // Find user by username or email
    const user = userData.find((user) => user['username'] === username || user['email'] === username);
    if (!user) {
      return res.status(401).json({ message: 'Username salah' });
    }

    // Check password
    const isPasswordValid = await compare(password, user.password);
    if (!isPasswordValid) {
      return res.status(401).json({ message: "password salah" });
    }

    // Create a JWT token
    const token = sign({ id: user.id, username: user.username }, SECRET_KEY, {
      expiresIn: '2h',
    });
    return res.status(200).json({ message: 'Login successful', token, id: user.id, username: user.username });
  });
  
  // Protected route
  router.get('/protected', (req, res) => {
    const token = req.headers['authorization'];
  
    if (!token) {
      return res.status(403).json({ message: 'No token provided' });
    }

    verify(token, SECRET_KEY, (err, decoded) => {
      if (err) return res.status(401).json({ message: 'Failed to authenticate token' });
      // Proceed with the request
      return res.status(200).json({ message: 'Access granted', userId: decoded.id });
    });
  });
  
  export default router;