You can get your chat id by sending message to the bot and go to this url to view the chat_id:
{{ telegramGetUpdatesURL }} {{ telegramGetUpdatesURL }}
"application/json" is good for any modern http servers such as express.js
"multipart/form-data" is good for PHP, you just need to parse the json by json_decode($_POST['data'])
You can check this url to view how to setup one:
https://github.com/bbernhard/signal-cli-rest-api
IMPORTANT: You cannot mix groups and numbers in recipients!
More info on: https://api.slack.com/messaging/webhooks