I'm assuming an onclick event counts as interacting with the document, so not sure why an autoplay error is being thrown
Uncaught (in promise) NotAllowedError: play() failed because the user didn't interact with the document first.
I was missing allow="autoplay" in iframe's attributes
<iframe id="video-player" class="video" width="560" height="315" src="https://player.vimeo.com/video/309741585" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen allow="autoplay"></iframe>