title: How to send a HTTP POST REQUEST by parameters using typescript
body: <p>I would like to send a POST request by param similar to that:</p>
  
  <pre><code>http://127.0.0.1:9000/api?command={"command":"value","params":{"key":"value","key":"value","key":"value","key":value,}}
  </code></pre>
  
  <p>I tried to do that, but not working:</p>
  
  <pre><code>    let command: HttpParams = new HttpParams();
      let params: HttpParams = new HttpParams();
  
      command = command.append('command', 'value');
  
      params = params.append('key', value);
      params = params.append('key', value);
      params = params.append('key', value);
      params = params.append('key', value);
      command = command.append('params', params.toString());
  
  
      this.httpClient.post('/api?', null, {
          params: command
      });
  
  
  The error is: 500 (Internal Server Error)
  </code></pre>
  
  <p>Could you please help me?</p>