Hello Ameer K,
Thanks for reaching out. There is no meeting endpoint hence you are receiving the error message. To send a chat message please use the example documented in article [https://learn.microsoft.com/en-us/graph/api/chatmessage-post?view=graph-rest-1.0&tabs=http](https://learn.microsoft.com/en-us/graph/api/chatmessage-post?view=graph-rest-1.0&tabs=http).
To retrieve messages for live events, use the chats messages endpoint as follows:
https://graph.microsoft.com/v1.0/user/{user-id}/chats/{live-meeting-chat-id}/messages
Please refer to article for more info.
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Thanks.