Hi Won,

Thank you for your question,

As headless bots are designed to perform execution of scripts on a scheduled basis or after a triggered event from an external system - you may need to review the scenario on how you plan on construct and use the headless bot.

If you plan on send messages by the headless bot to provide information to the chatrooms which the headless bot is already a member of - then you can use the following REST API endpoint (https://developers.symphony.com/restapi/reference/list-user-streams) to firstly obtain the list of 'StreamID' and then sending the message to those chatrooms.

Please let us know if you have any further questions.
Kind regards
Kaosar