[Bug]: ValidationError on MessageActivity

[jerbob92]

Bug Description

It looks like this MR broke the bot integration for a few of our users. It seems that not all webhooks that currently go out have the required App info.

This is what the payload looks like:

{
  attachments: [
    {
      content: "<p>/stop</p>",
      contentType: "text/html"
    }
  ],
  channelId: "msteams",
  from: {
    aadObjectId: "xxx",
    id: "xxx",
    name: "xxx"
  },
  id: "xxx",
  localTimestamp: "2026-08-17T09:41:58.4117934+02:00",
  serviceUrl: "https://smba.trafficmanager.net/emea/xxx/",
  text: "/stop",
  textFormat: "plain",
  timestamp: "2026-08-17T07:41:58.4117934Z",
  type: "message"
}

As you can see, no App info.

Steps to Reproduce

1. Message the bot (but I don't know how to exactly reproduce this).
2. Get a validation error

Expected Behavior

No error.

Actual Behavior

Error:

1 validation error for tagged-union[TypingActivity,CommandSendActivity,CommandResultActivity,ConversationUpdateActivity,MessageActivity,MessageDeleteActivity,MessageReactionActivity,MessageUpdateActivity,tagged-union[ReadReceiptEventActivity,MeetingStartEventActivity,MeetingEndEventActivity,MeetingParticipantJoinEventActivity,MeetingParticipantLeaveEventActivity],tagged-union[FileConsentInvokeActivity,ExecuteActionInvokeActivity,MessageExtensionAnonQueryLinkInvokeActivity,MessageExtensionCardButtonClickedInvokeActivity,MessageExtensionFetchTaskInvokeActivity,MessageExtensionQueryInvokeActivity,MessageExtensionQueryLinkInvokeActivity,MessageExtensionQuerySettingUrlInvokeActivity,MessageExtensionSelectItemInvokeActivity,MessageExtensionSettingInvokeActivity,MessageExtensionSubmitActionInvokeActivity,ConfigFetchInvokeActivity,ConfigSubmitInvokeActivity,TabFetchInvokeActivity,TabSubmitInvokeActivity,TaskFetchInvokeActivity,TaskSubmitInvokeActivity,MessageFetchTaskInvokeActivity,MessageSubmitActionInvokeActivity,HandoffActionInvokeActivity,SignInTokenExchangeInvokeActivity,SignInVerifyStateInvokeActivity,SignInFailureInvokeActivity,AdaptiveCardInvokeActivity,SuggestedActionSubmitInvokeActivity,SearchInvokeActivity,HtmlWidgetCallToolInvokeActivity],tagged-union[InstalledActivity,UninstalledActivity]]
message.channelData.app.id
  Field required [type=missing, input_value={}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.13/v/missing

SDK Version

2.0.15

Python Version

3.14.7

Additional Context

No response

[jerbob92]

Extra info: this only seemed to occur for 1 specific user in DM (I can share details privately if needed), we fixed the issue by rightclicking the app and clicking Uninstall and then installing it again for the user. Maybe this is some backend hickup?

[jerbob92]

I just had someone else that also had this issue, it could be this issue will start to appear for more users soon?

[corinagum]

Hey jerbob92, thanks for reporting this bug.

#504 added AppInfo to ChannelData with a required id. channelData.app is optional, so a missing app would be fine, but the service can send channelData.app as an empty o bject, and Pydantic would then fail on the missing id. This causes the entire activity to be rejected, which is why the bot goes silent.

Same applies to channel, team, etc. on inbound activities.

You're also correct about this possibly affecting more customers going forward. app object is currently gated behind a rollout and only applies to 1:1 chats. As that rollout ramps up, more customers may hit this until the SDK fix ships.

Workaround

• uninstall/reinstall that you mentioned does work, and resets the affected user
• Pinning below the release that caused this break (microsoft-teams-*<2.0.15) until the fix is released

Fix

Make id optional in AppInfo, ChannelInfo, TeamsInfo, TenantInfo, and selectedChannel, and add test coverage for the case of any of these being an empty object. I'll also discuss with the service team about when these can come in as an empty object.

[jerbob92]

Thanks, will downgrade to 2.0.14 for now.
Too bad, because that had some other things that I wanted.

[corinagum]

jerbob92 2.0.16 has been released, thanks for your patience.