Update existing file in repository giving 400 error in rest template

I am trying to edit existing file in a repo using gitlab v4 api, When I tried to edit file using postman rest client it executes without any issue, 200 status returned. When I tried the same with SpringBoot RestTemplate, I am always ending up with 400 bad request error. I am completely dont know what actually happening. Rest URL is : https://domain name/api/v4/projects/51/repository/files/src%2Fmain%2Fresources%2Fapplication.yml

Request body is : [branch=master, content=server: port: value, commit_message=port number updated, file_path=src%2Fmain%2Fresources%2Fapplication.yml]