I confirm that the problem is the 10 minutes of inactivity. uptimerobot tries to ping it, but you didn’t set up any http server in your app, so uptimerobot doesn’t receive any response and stops trying.
Basically, you know you’re done when the “Show” button stops spinning. To do that, you’ve to setup an http server, for example using express. It’s very easy. Somewhere at the beginning of your server.js file, you can write this:
const express = require("express")
const expressApp = express()
expressApp.get("/", (req, res) => res.json("OK"))
expressApp.listen(process.env.PORT)
trigger a restart, and you should be good to go!