First, you need to verify the option autoplay is well activated and that the story is published.
There are few reasons why videos may not autoplay on a website:
The website's code may have been configured to not allow videos to autoplay.
The browser being used may have a setting that disables videos from autoplaying.
Some videos may be blocked by the browser's built-in ad blocker.
Some devices, like mobile devices, may not support autoplaying videos.
The video hosting platform may not have the feature enabled for the specific video.
It's important to note that many browsers and devices now block autoplaying videos by default to improve user experience and save on data usage. Additionally, some users may have restrictive personal preferences set.
Did you use an Iframe
You must not forget to add the "allow" attribute