Error While using RASA with REST API

Hi , i’m new to rasa , i had followed the rasa for beginner udemy course and using the code from it and the chatbot works completely fine when using rasa shell. I tried to experiment making POST request from POSTMAN using REST API with a json body with sender=“send_01” and message:“Hi” , it works . But when everytime i tried make a POST request with message:“yes” (matching with affrim intent) . Some error shows up in the server as seen below. I can’t figure what is the problem . Hope someone from the community forum is possible the assist me on it Thanks .

Github Repo for the udemy course : GitHub - RasaHQ/rasa-for-beginners at 2-0-migration