If you have added your YouTube Livestream to SpatialChat, but other users are unable to view it, there could be a few explanations for this.
One potential explanation for the issue could be that your video is not set to be embeddable. To resolve this, you can go to your video's settings and check the appropriate box to allow it to be embedded. This should allow other users to view your YouTube Livestream on SpatialChat.
If the issue persists even after allowing your video to be embedded, there may be other potential causes. According to some sources, new YouTube accounts may need to be in good standing in order for their videos to be embedded on other websites. Typically, an account is considered to be in good standing if it has at least 1000 subscribers and 4000 hours of views on its videos. If your account does not meet these criteria, you may still be able to enable the embedding of your streams on other websites by enabling AdSense (monetization) on your account. To do this, you can follow the instructions provided in the linked article.
If the above steps do not resolve the issue and you are still unable to embed your YouTube Livestream on SpatialChat, you can try following the tutorial provided in the linked article to enable the embedding of live streams from YouTube. This process may take up to 7 days for YouTube to review and allow embedding on your account.