title: Preflight response is not successful with proper headers
body: <p>I'm having issue getting my ionic app to POST to my API. On my api I have set the following headers:</p>
  
  <pre><code>header("Access-Control-Allow-Origin: *");
  header("Access-Control-Allow-Headers: Content-Type");
  header("Access-Control-Allow-Methods: GET,PUT,POST,DELETE,OPTIONS");
  </code></pre>
  
  <p>When posting from Postman or the actual website, everything functions as expected and I see these headers come back but once I open up my app and send a request, it no longer works. </p>
  
  <p>GET Requests are working fine, it's just POST requests that are broken. I use the following to send a post request on my app:</p>
  
  <pre><code> /**
    * Post to the API
    * @param path    Where to go
    * @param params  What to send
    */
   private post(path, params): Promise&lt;any&gt; {
     return this.http
       .post(this.apiUrl + path, params)
       .toPromise()
       .then(r =&gt; r.json());
   }
  </code></pre>
  
  <p>I get the following error inside of my ionic app</p>
  
  <pre><code>Failed to load resource: Preflight response is not successful
  XMLHttpRequest cannot load https://mmcalc.com/api/calculate. Preflight response is not successful
  </code></pre>
  
  <p>I've been pulling my hair out over this for nearly 15 hours now, I don't understand why it won't work. </p>