Hello Daniel Camcho,
Thank you for reaching out to Microsoft!!
While posting message to channel in Teams using Graph API, if you want to update the chat page as soon as the message is sent by API, could you try using the Delegated permissions in the Graph Explorer as I am able to see the message in channel while using the Graph API with delegated permissions.
Please try executing the Graph API using Graph Explorer by signing in as a user.
Hope this helps.
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