Teams Desktop/Web shows "Unable to reach app" for Adaptive Card action — works on Mobile

Hi @Nariman NAHMADOV

Based on the details you provided, I understand that your Teams bot is successfully processing Adaptive Card actions (HTTP 200), but the Desktop and Web clients are displaying the "Unable to reach app" error despite the card updating correctly.

Recent updates to the Teams Desktop and Web clients have made response handling much stricter compared to the Mobile client. While Mobile may only look for a successful HTTP 200 status, Desktop/Web also validates the structure and timing of the response payload. If the format isn't exactly what the client expects or if the response takes too long, the UI will trigger a timeout error even if the action was technically processed.

Teams Desktop/Web requires a specific JSON structure for invoke activities. Ensure your bot is returning the updated card in the response body immediately. A standard successful response should look like this:

{
  "statusCode": 200,
  "type": "application/vnd.microsoft.card.adaptive",
  "value": { 
    "type": "AdaptiveCard",
    "version": "1.4",
    "body": [ /* Your updated card JSON here */ ]
  }
}

If you are currently using Action.Submit, I recommend migrating to Universal Actions (Action.Execute). Universal Actions were designed to provide a consistent experience across all platforms. They handle loading states much better and are the preferred method for modern Teams bot development.

You can find the implementation details here: Universal Actions for Adaptive Cards.

Teams expects an invoke response within 5 seconds. If your bot performs heavy processing before returning the updated card, the Desktop client might "give up" and show the error. Ensure you are sending the response as quickly as possible.

I hope this helps resolve the inconsistency! Please let me know if you need more details.

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