Kakao message rest api 400 error

Hello, everything I have tried has resulted in a 400 error. I am trying to send a message to a single user who is a member of my developer team. I have retrieved the uuid by using the /me api. But I am getting 400 bad request errors every single time. Is there separate authorization I need?

Project ID 1043306

The UUID used is not obtained through the Friend Picker or “/v1/api/talk/friends”.

In a separate thread, you told me I could obtain the UUID through the me API. I got the UUID there, but still cannot send a message. I am not using the friendpicker or friends API. My end goal is to send messages to only one single user.