The "Source not supported" error in Chrome may appear if the browser or Chromecast cannot identify the source content you are trying to cast.
Chromecast Not Working? 6 Tips to Fix Your Chromecast Issues
There are several possible reasons for this error, and therefore several possible solutions. For example, it could be a browser hiccup, an issue with the Chromecast itself or your network, or anything from incompatible software to disabled settings.
Here’s what to do if you see this error in Chrome. These steps should work no matter what you’re trying to cast, whether it’s a streaming video, a local file, or your entire desktop or browser tab. Remember to test to see if the solution worked for you before moving on to the next step.
Unplug the Chromecast, or the TV if it has a built-in power source, from the power outlet for a few seconds and then plug it back in.