title: React Native - Fetch POST not working
body: <p>I am having huge troubles getting my fetch POST calls to work on iOS. My standard Fetch calls work and the Fetch POST calls work fine on android but not iOS.</p>
  
  <p>The error that comes up is "Possible Unhandled Promise Rejection (id: 0): Unexpected token &lt; in JSON at position 0"</p>
  
  <p>It actually saves the post data to my server but throws that error.</p>
  
  <p>I tried debugging the network request using <code>GLOBAL.XMLHttpRequest = GLOBAL.originalXMLHttpRequest || GLOBAL.XMLHttpRequest;</code> before the API call coupled with using CORS in my chrome debug tools. From there I can see that it is making two post calls one after the other. The first one has type "OPTIONS" while the second one has type "POST". It should probably be noted that the call works in the App while using CORS and the line of code above.</p>
  
  <p>I'm very confused and have exhausted all avenues.</p>
  
  <p>My code im using for refrence is as follows.</p>
  
  <pre><code>return fetch(url,{
          method: 'post',
          headers: {
              'Accept': 'application/json',
              'Content-Type': 'application/json'
          },
          body: JSON.stringify(data)
      }).then((res) =&gt; res.json());
  </code></pre>