The default behavior is to use polling to fetch telegram bot messages because this does not require setting up SSL certificates on the bot server. If you'd still like to use webhooks, the following might be helpful:

To run this bot locally, use ngrok or npm's localtunnel:

ngrok http 3000 # inspect on https://localhost:4040/inspect/http
# https://123456.ngrok.io -> https://localhost:3000
# set https://123456.ngrok.io as WEBHOOK_DOMAIN in .env
npm start

Setting the webhook environment variables and starting the bot then changes the bot's webhook URL settings.

This should no be done with the official bot as it changes the webhook URL. You can create a new Telegram bot just for testing