title: Getting Let's encrypt cerificate to work with android api < 20
body: <p>I have a node server which uses Let's Encrypt CA and it's hosted on zeit.now.
  The client is developed using react-native.
  I try to connect to it using websockets.</p>
  
  <p>On iOS and newer Android versions (API > 20) it connects successfully.</p>
  
  <p>When running on older Android versions (both on simulator and actual devices) it never connects.</p>
  
  <p>I have tried to connect using older Android version to a server that's not using Let's encrypt CA (but IS using ssl from other provider - hosted on heroku), and it also connects successfully.</p>
  
  <p>So I believe there is something wrong with older Android versions and Let's encrypt certificate.</p>
  
  <p>Could someone help? I have lost 5 days researching this problem and I don't know a lot about JAVA.</p>
  
  <p>EDIT:
  I try to connect using websocket</p>
  
  <pre><code>    ws.onerror = (e) =&gt; {
        // an error occurred
        console.log(e.message);
      };
  </code></pre>
  
  <p>this logs:</p>
  
  <pre><code>Connection closed by peer
  </code></pre>
  
  <p>and this method:</p>
  
  <pre><code>    ws.onclose = (e) =&gt; {
        // connection closed
        console.log(e.code, e.reason);
      };
  </code></pre>
  
  <p>logs:</p>
  
  <pre><code>undefined, undefined
  </code></pre>