Cannot POST /users/add in insomnia and postman

Question

Here is my user schema:

const mongoose=require('mongoose');
const userSchema=new mongoose.Schema({
username:{
    type: String,
    required: true,
    unique: true,
    minlength: 3,
},
password:{
    type: String,
    required: true,
    minlength: 8
}
})
const User=mongoose.model('User', userSchema);
module.exports = User;

And here is my users router:

const router = require('express').Router();
const bodyParser = require('body-parser')
let User= require('../models/userSchema');
router.route('/').get((req,res)=>{
User.find()
.then(users => res.json(users))
.catch(err => res.status(400).json('Error:'+err));
});
router.route('/add').post((req,res)=>{
const username=req.body.username;
const password=req.body.password;
const newUser=new User({username, password});
newUser.save()
.then(()=>res.json('User added!'))
.catch((err)=>res.status(400).json('Error:'+err));
});
module.exports=router;

Whenever I post this in insomnia or postman, I get an error Cannot POST /users/add even though I'm successfully connected to server and to MongoDB

{
"username":"John",
"password":"password1234"
}