HTTP / 1.1 400错误请求Delphi VCL XE6

I have to send by post to a URL string of JSON text, I use a TidHTTP component for sending by post as shown in the code below, but when I hit the submit button I skip this error, I've been searching google to another people that this happens but none of the solutions have helped me in this case.I have to send by post to a URL string of JSON