Installing node via HTTP Post not working

I'm trying to install a node using the HTTP API:
I tried with several HTTP clients, like Postman but I'm getting the following error:


And if I try to use Java API I get the same HTTP 400 error: Server returned HTTP response code: 400 for URL: http://localhost:1880/nodes

HTTP 400 indicates that there is a problem with the request itself but I can't see it, it seems to be the same as the example from the web page.

Any ideas? Thanks!