title: how to send a POST request to download a file using rn-fetch-blob?
body: <p>I'm using <a href="https://github.com/joltup/rn-fetch-blob" rel="nofollow noreferrer">rn-fetch-blob</a> library to download and save a file into the device, and I've been successful to do it with GET request like: <code>.fetch('GET', "http://api.pdflayer.com/api/convert?access_key=MY_ACCESS_KEY&amp;document_url=URL_PATH")</code>, but the API that I use just accepts post request, so I tried this but didn't work:</p>
  
  <pre><code>const { config, fs } = RNFetchBlob;
  let DownloadDir = fs.dirs.DownloadDir;
  let options = {
    fileCache: true,
    addAndroidDownloads : {
      useDownloadManager : true,
      path: DownloadDir + "/file.pdf"
    }
  };
  const data = JSON.stringify({
    access_key: "MY_ACCESS_KEY",
    document_url: "https://pdflayer.com/downloads/invoice.html"
  });
  config(options)
    .fetch('POST', 'http://api.pdflayer.com/api/convert', {body: data})
      .then((res) =&gt; {
         console.log(res);
      })
      .catch((err) =&gt; {
         console.log(err)
      })
  </code></pre>
  
  <p>If I'm not sending my request correctly, so how should I do it? thanks in advance.</p>