CODE EXAMPLE FOR HTML

youtube iframe autoplay not working

<iframe id="existing-iframe-example"
          width="640" height="360"
          src="https://www.youtube.com/embed/-SFcIUEvNOQ?autoplay=1&mute=1&enablejsapi=1"
          frameborder="0"
          style="border: solid 4px #37474F"
          ></iframe>