I found this bug in `Maximum` program on Hackerone.
The chatting endpoint was missing rate limit protection, allowing attackers to send unlimited messages to the CHAT bot and causing denial of service which in order will crash CHAT bot and deny it from responding to users.
DOS & Denying Chat Bot from responding to users.
Create a message, send it and intercept its request. Send that request to intruder.
Launch the attack. So now the same request is being replayed and sent unlimited times.
CHAT bot system will crash. So now try to send a message to that CHAT bot. No reply will present.