1) Open Telegram and send any message to your bot.
2) Paste your bot token below (from @BotFather).
3) Click Get Updates. Your chat_id will appear as chips and inside the JSON.
{ }
If you see {"ok":false,"error_code":404,"description":"Not Found"} that means the URL or token is wrong.
Make sure you are calling https://api.telegram.org/bot<TOKEN>/getUpdates (note the word bot).