Teams error 401 Unauthorized (invalid app ID / password): Invalid Microsoft App ID or password

Your bot could not exchange its credentials for an access token, so every outbound Connector call - and, on the inbound side, every attempt to validate that requests really come from the Bot Framework - fails with 401. The failure lives in the appId / password / tenant triangle: the Microsoft App ID (a Microsoft Entra application), the client secret issued for that application, and the tenant the token request is sent to. All three must agree. A perfectly valid secret paired with the wrong app ID fails; a valid pair sent to the wrong tenant endpoint fails; and each corner fails with a different AADSTS code in the token response body.

The two you will actually see: AADSTS7000215, which the Microsoft Entra error reference describes as "Invalid client secret is provided" - very often because the secret ID column was copied from the portal instead of the secret value, which is only shown once at creation - and AADSTS700016, "The application wasn't found in the directory/tenant", which means the app ID itself is wrong for the tenant you are authenticating against (see the tenant mismatch entry when the ID is right but the tenant is not).

Because the token exchange happens before Teams is involved, the user-visible symptom is pure silence: messages send, the bot never replies, and nothing appears in Teams itself. Your service logs show the 401 either at adapter startup or on the first reply attempt.

{
  "error": "invalid_client",
  "error_description": "AADSTS7000215: Invalid client secret provided. ...",
  "error_codes": [7000215],
  "timestamp": "2026-08-20 09:14:02Z"
}

Store the secret in a secrets manager and validate credentials at startup by requesting one token, failing the deploy loudly on 401 instead of shipping a bot that cannot speak. Record which app ID each environment uses next to the secret so the triangle can be audited in one place. The token cURL test in the fix list is cheap enough to run in CI on every release; Microsoft's own troubleshooting guide makes it step 2 of four. Silent credential drift is cause 2 in Teams bot not responding.