Teams API returns unauthorized error despite valid app registration

Question

When calling Microsoft Teams APIs from a custom app, Ive got 401 Unauthorize error.

The app uses OAuth 2.0 with delegated permissions, and access tokens are issued successfully, but Teams API calls (such as sending messages or accessing chat data) fail with an authorization error.

Answer 1

Hi Madril Johanna

Thank you for reaching out to Microsoft Q&A Forum and sharing your experience regarding the unauthorized error you are facing with the Microsoft Teams API.

I understand how confusing it is to receive a 401 Unauthorized response even though your application successfully retrieves an access token. This scenario typically suggests that the token is technically valid but lacks the specific authorization required for the Teams resource you are accessing.

I recommend starting your troubleshooting by inspecting your access token using a tool like jwt.ms to verify the internal claims. Please confirm that the audience claim matches the API you are calling, which is usually https://graph.microsoft.com for these requests. You should also check the scopes claim to ensure it explicitly lists the permissions required for the specific action you are trying to perform.

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Another common cause for this behavior is missing required permission consent. Please navigate to the API Permissions section in your Azure Portal app registration and ensure that the status column shows a green checkmark indicating consent has been granted for your tenant. Since you are using delegated permissions, it is also important to verify that the signed user has a valid Teams license and access to the specific chat or team context.

Please let me know how you get on, as your feedback is valuable to the community. 

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