How do I place a Node application on Heroku that runs full-time and is not an api?

Question

Objective: to run Puppeteer on Heroku for at least 8 hours a day, without interruptions.

I have a simple program on Puppeteer, it basically operates some accounts on websites and that’s it. That’s it. Does not return value, or use database, or create ports. The maximum is a request to an external api via Xios.

During the run I went through some boring problems: browser not wanting to start, Node packages missing, and so on. Nothing too complicated.

Finally, I had two problems:

• Using "web: Node index.js" in Procfile without express

Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch
Stopping process with SIGKILL  
Process exited with status 137  
State changed from starting to crashed

• Using the same web command, but with express:

    The addition of code

const app = express()

app.get('/', function (req, res) {
    res.send("it's working")
})

app.listen(process.env.PORT || 3000)

    The mistake

Idling 
State changed from up to down
Stopping all processes with SIGTERM
Error R12 (Exit timeout) -> At least one process failed to exit within 30 seconds of SIGTERM
Stopping remaining processes with SIGKILL
Process exited with status 137