Cannot use post on NodeJS

So I'm trying to insert 3 strings from postman to my mongo database using the api localhost:3000/api/comment/

my database is on mongodb://localhost:27017/commentbox

and my server.js contains

var express = require('express');
var morgan = require('morgan');
var bodyParser = require('body-parser');
var config = require('./config');
var mongoose = require('mongoose');

var app = express();

app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(morgan('dev'));

var api = require("./app/routes/api")(app, express);

api.use('/api', api);

app.get('*',(req, res)=>{
    res.sendFile(__dirname + '/public/views/index.html');
});

mongoose.connect(config.database, { useNewUrlParser: true },(err)=>{
    if(err){
        console.log(err);
    }else{
        console.log('Connected to DB');
    }
});



app.listen(config.port, (err) =>{ 
    if(err){
        console.log(err);
    }else{
        console.log('Listening on port:'+ config.port);
    }
});

and this is the code for my api.js

var User = require('../models/user');


module.exports = function(app,express){

    var api = express.Router();

    api.post('/comment', function(req,res){
        var user = new User({
            name: req.body.name,
            comment: req.body.comment,
            date: req.body.date
        });

        user.save(function(err){
            if(err){
                res.send(err);
                return;
            }

            res.json({ message: "User has commented"});
        });
    });

    return api;
}

when I try to post on postman with name, comment, date (btw this are 3 strings at the moment) I always got error 404

what should be the problem? I have followed the guide thoroughly