Hi @Hsiao_Min_Shyh, that's an interesting question. I haven't seen anyone else integrating Chatwoot with Retool so we don't have any pre-existing info on common pitfalls. We do have this page on embedding apps, which includes info on the process, whether you're embedding within Retool or a Retool app is being embedded.
One thing to note is that the js docs on postMessage warn about using '*' as a target origin due to potential security vulnerabilities, so you might want to use either your apps url or your retool url for that value.
Also, you'll want to use Retool's functionality to receive these messages. Retool does not support using event listeners. As shown in a previous link, you can try to use a ParentWindow Resource to read those values.