In order to get the group chat id, do as follows:

1. Add the Telegram BOT to the group.

2. Get the list of updates for your BOT:

   https://api.telegram.org/bot<YourBOTToken>/getUpdates
   

   Ex:

   https://api.telegram.org/bot123456789:jbd78sadvbdy63d37gda37bd8/getUpdates
   

3. Look for the "chat" object:

{"update_id":8393,"message":{"message_id":3,"from":{"id":7474,"first_name":"AAA"},"chat":{"id":,"title":""},"date":25497,"new_chat_participant":{"id":71,"first_name":"NAME","username":"YOUR_BOT_NAME"}}}

This is a sample of the response when you add your BOT into a group.

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