title: How to resolve an ok 200 error when integrating slack incoming webhook with angular 4.2.4?
body: <p>As soon as I click the button to submit the message to slack, I receive the following error message. The message is however successfully sent to the slack channel. The error comes into play upon the subscribe method. I tried removing the subscribe method, but since observable can't run without it, I had to use it.</p>
  
  <p>Error Message:          </p>
  
  <pre><code>HttpErrorResponse {headers: HttpHeaders, status: 200, statusText: "OK", url: "https://hooks.slack.com/services/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", ok: false, …} .   
  error:{error: SyntaxError: Unexpected token o in JSON at position 0 at Object.parse (&lt;anonymous&gt;) at XMLHt…, text: "ok"} .  
  headers:HttpHeaders {normalizedNames: Map(0), lazyUpdate: null, lazyInit: ƒ} .  
  message:"Http failure during parsing for https://hooks.slack.com/services/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" .  
  name:"HttpErrorResponse"
  ok:false
  status:200
  statusText:"OK"
  </code></pre>
  
  <p>Angular4 Code:</p>
  
  <pre class="lang-js prettyprint-override"><code>const payload = JSON.stringify({"text": "Hihi",});  
    const headers = new HttpHeaders().set('Content-type', 'application/x-www-form-urlencoded; charset=UTF-8');  
    this.http.request(
      'POST',
      "https://hooks.slack.com/services/TOKEN",
      {
        'body': payload,
        'headers': headers,
      }
    ).subscribe();
  </code></pre>