We are tracking an issue where changing password can result into it taking a long time to get access to the API again (upto 1 day). For now if you wait for a day you should get access to the API again.
Authentication errors when sending messages to Teams

The API is used in the following process.
- get token
- send a message to Teams using the obtained token
However, after you change the password of your Microsoft account, you will not be able to send messages to Teams.
You can get a token or update it with a refresh token.
The following APIs will generate error Unauthorized.
https://graph.microsoft.com/v1.0/teams/{team_id}/channels/{channel_id}/messages
If I change the password of my Microsoft account, will I not be able to use the Teams API?
I would appreciate it if someone could tell me.
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Vasil Michev 70,486 Reputation points MVP
2021-09-28T09:21:35.693+00:00 Microsoft (personal) accounts are not supported for that endpoint, as documented here: https://learn.microsoft.com/en-us/graph/api/channel-post-messages?view=graph-rest-1.0&tabs=http
You need to use a work/Office 365 account. Other than that, make sure you have the required permissions.