The error No web processes running is pretty clear; you either do not have a web process defined in your Procfile meaning there is no server that can respond to incoming requests, OR you have your web processes scaled to 0.

You will need to create or update your Procfile to contain a web process that starts your Discord bot server.

web: <command to start server> -p $PORT

If that is already configured, you will need to ps:scale your process using the Heroku CLI.

heroku ps:scale web=1