I need to automate sending messages in some teams channels. I use the POST method on endpoint “https://graph.microsoft.com/v1.0/teams/{teamId}/channels/{channelId}/messages”. My JSON looks like this :

"from": {
    "application": {
        "@odata.type": "#microsoft.graph.teamworkApplicationIdentity",
        "id": appId,
        "displayName": appName
    }
}

When I run this request in a Python script, I receive a 400 error and the body says “Invalid request – User is missing.”. If I try to add “user” in the “from” dictionnary with a valid user Id, I receive a 400 error with message “Only one of user, application, conversation or tag must be specified in identitySet”.

Thus, my question is how can I send a message using my Azure App in a channel ?
I checked and my app has all the permissions needed.
If the problem come from the token, I get it from the msal library :

app = ConfidentialClientApplication(clientId, authority=f"https://login.microsoftonline.com/{tenantId}", client_credential=clientSecret)
result = app.acquire_token_for_client(scopes=["https://graph.microsoft.com/.default"])