Embedding Content - waveform.social

I am working on a small web app to allow sharing audio and videos on my instance. I read that lemmy supports embedding pages that provide opengraph metadata. To test this I created a simple page: https://chappio.gitlab.io/embed-demo/ [https://chappio.gitlab.io/embed-demo/] But when I post it, no content gets embedded. My goal is to provide an embeddable widget to my instance. What am I missing?