You will need to stringify your JSON data so that you can pass the JSON in body as a string something like below so that you can pass this string the BODY as a string.
I had the following response (there is no id generated like in postman):
<!--
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Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
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Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>Gravitee.io Portail</title>
<base href="/" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<link rel="shortcut icon" href="favicon.ico" />
<link rel="icon" type="image/png" href="favicon.png" sizes="96x96" />
<script src="webcomponents/webcomponents-loader.js"></script>
<link rel="stylesheet" href="styles.e0626c0f9f0284497b30.css"></head>
<body>
<gv-spinner id="loader"></gv-spinner>
<app-root></app-root>
<script src="runtime-es2015.33e625c09ce899a4e012.js" type="module"></script><script src="runtime-es5.33e625c09ce899a4e012.js" nomodule defer></script><script src="polyfills-es5.a1e3e93b0d43c59dbb37.js" nomodule defer></script><script src="polyfills-es2015.8ea7045f2d75fc02ed20.js" type="module"></script><script src="scripts.9b9151f02d2cc705805c.js" defer></script><script src="main-es2015.7ef12a4f4b7aa5ae50ea.js" type="module"></script><script src="main-es5.7ef12a4f4b7aa5ae50ea.js" nomodule defer></script></body>
</html>