In Postman v11.81.1, when sending a POST request with the body set to raw JSON, the Content-Type is set to 'Content-Type: application/json, charset=utf-8'
Hey @wr307209868 
Welcome to the Postman Community 
I’m not sure about the issue you’re reporting here - Is it that header is causing a request to fail? Does the request succeed if you edit the header before sending?
If you could provide more information and context, that would help us to assist you further.