Get chat id from Telegram bot

1- Add the bot to the group.
Go to the group, click on group name, click on Add members, in the searchbox search for your bot like this: @my_bot, select your bot and click add.

2- Send a dummy message to the bot.
You can use this example: /my_id @my_bot
(I tried a few messages, not all the messages work. The example above works fine. Maybe the message should start with /)

3- Go to following url:
replace XXX:YYYY with your bot token

4- Look for “chat”:{“id”:-zzzzzzzzzz,
-zzzzzzzzzz is your chat id (with the negative sign).