Node.js Discord bot works in localhost, but not when deployed to firebase hosting

Question

The exact project works in localhost, but not when deployed to Firebase.

With postman, when I send post request to /new-sub in localhost with a body, the bot messages to a specific channel in a specific server. When I send the same request to the live url, I get 404 instead.

Why does it behave differently when deployed?

my code:

const { Client, GatewayIntentBits } = require('discord.js');
const express = require("express");
const app = express();
app.use(express.json());

const token = "xxx";

const client = new Client({
    intents: [
        GatewayIntentBits.Guilds,
        GatewayIntentBits.GuildMessages
    ]
});
client.login(token); 

const port = process.env.POST || 443;
app.listen(port, () => {
    console.log(`Project is running. Listening on port ${port}`);
});

app.get("/", (req, res) => {
    res.send(`hello world. Port: ${port}}`);
});

app.post("/new-sub", (req, res) => {
    const [body, query] = [req.body, req.query];


    const guildId = query.guildId || "1234";// server id
    const channelId = query.channelId || "5678";
    const guild = client.guilds.cache.get(guildId);
    if (!guild) {
        const errMsg = `<p>Guild ${guildId} not found</p>`;
        console.log(errMsg);
        res.send(errMsg);
        return;
    }

    const channel = guild.channels.cache.get(channelId);
    if (!channel) {
        const errMsg = `<p>Channel ${channelId} not found in ${guild.name} (${guildId})</p>`;
        console.log(errMsg);
        res.send(errMsg);
        return;
    }

    const newMessage = `New sub! Title: ${body.title}, time: ${new Date(Date.now())}`;
    console.log(newMessage);
    channel.send(newMessage);

    console.log(`message sent to ${channel.name} channel in ${guild.name}`);
    res.send(newMessage);
});

app.use(express.static('public'));