Teams channel on bot returns "Failed to decrypt conversation id" after channel re-added

ben_mgrmis 0 Reputation points
2026-09-21T11:36:18.5133333+00:00

Our Teams bot stopped receiving Teams messages after a server outage . The messaging endpoint was updated and verified: Web Chat delivers successfully (HTTP 200) and the bot can send proactive messages to Teams. Teams did not attempt delivery at all, which appeared to be a channel backoff. We then deleted and re-added the Microsoft Teams channel. Since then, every Teams message fails with "Failed to decrypt conversation id", including after removing and reinstalling the app. Please reset the Teams channel state and/or conversation mappings for this bot so existing personal-scope conversations can be decrypted again.

Azure AI Bot Service
Azure AI Bot Service

An Azure service that provides an integrated environment for bot development.

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  1. AI answer

    2026-09-21T11:36:32.6366667+00:00

    Deleting and re-adding the Teams channel is the likely cause. Re-enabling a deleted Teams channel generates a new pair of keys, which invalidates stored 29:xxx and a:xxx IDs used for proactive messaging. The documented guidance is to restart the Microsoft Teams channel, not delete and re-add it.

    For the current state:

    1. Stop relying on previously stored Teams conversation references and IDs for personal-scope conversations.
    2. Re-establish fresh conversation context for affected users, then update the stored conversation ID/reference.
    3. If a conversation is no longer valid, treat it as stale and reacquire a fresh conversation context before retrying.
    4. If Teams returns BotNotInConversationRoster, reinstall the app in the conversation and wait for an installationUpdate event before sending again.
    5. If Teams returns ConversationNotFound, remove the cached conversation ID and replace it with a newly acquired one.

    For the original outage pattern where Teams stopped delivering to the bot while the tunnel/endpoint was healthy, the supported remediation is:

    1. In Azure portal, open the bot's Azure Bot resource.
    2. Go to Channels.
    3. Restart the Microsoft Teams channel.
    4. Send a test message and verify inbound activities resume.

    Important caution: deleting and re-adding the Teams channel regenerates keys and invalidates stored conversation identifiers. That is why restarting is recommended instead of deleting the channel.

    No documented self-service reset is provided for restoring decryption of existing conversation IDs after the Teams channel has been deleted and re-added. The supported path in the available guidance is to rebuild conversation state by reacquiring fresh conversation references and reinstalling where needed.

    AI-generated content may be incorrect. Read our transparency notes for more information.

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