title: POST fails with ReadableNativeMap cannot be cast to String error
body: <p>I'm working in <code>React Native</code>, I use <code>PHP</code> for backend and when I use fetch <code>POST</code> request I get so strange error, and I dont know why it happens. I checked the url so it works no problem, also normal <code>fetch()</code> is working without <code>POST</code> but when I try to post it happens. When I try it in local server fetch <code>POST</code> works.. but in server, I get this error :</p>
  <blockquote>
  <p>ERROR : com.facebook.react.bridge.ReadableNativeMap cannot be cast to
  java.lang.String</p>
  </blockquote>
  <p>React native codes :</p>
  <pre><code>fetch('http://xxx/react_test1', {
    method: 'POST',
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      name: inputName,
      email: inputEmail,
      phone: inputPhone
    }),
  }).then((response) =&gt; response.json())
    .then((responseJson) =&gt; {
      Alert.alert(responseJson);
    }).catch((error) =&gt; {
    alert(error);
  });
  </code></pre>