Power Platform Community Forum Thread Details

Summary

The Power Automate action “Post message in a chat or channel” consistently fails with 400 BadRequest – UnknownError even though the message is successfully created in Microsoft Teams. This breaks downstream logic that depends on the action’s outputs (e.g., message ID, webUrl) for subsequent updates.

Impact

Flow run shows a red‑X, causing conditional branches and error handling to trigger unnecessarily.

Metadata required for follow‑up actions (e.g., updating the original post, linking to the Teams message) is unavailable because the connector does not return the expected response object.

Operational automation is degraded; workarounds introduce complexity and risk.

Repro Steps

Action: Teams → Post message in a chat or channel
- poster = User
- location = Channel
- Parameters:
  - groupId = 3b51e7d4-b8ba-425e-8b11-be85c83241fa
  - channelId = VoiceApps Deployment Tracker Automation
  - messageBody = HTML table (built via concat())

Run flow.

Observe:

Message appears in Teams:

https://teams.microsoft.com/l/message/19:xCmcghsCq-GAkwGr2YyU48K2sr7RkaNX_7BpaCvXc7Q1@thread.skype/1762049415635?tenantId=72f988bf-86f1-41af-91ab-2d7cd011db47&groupId=3b51e7d4-b8ba-425e-8b11-be85c83241fa&parentMessageId=1762049415635

Flow action fails with:

{
"statusCode": 400,
"headers": {
"Transfer-Encoding": "chunked",
"Vary": "Accept-Encoding",
"Strict-Transport-Security": "max-age=31536000",
"request-id": "ed77306f-fc7a-42ca-820a-976809140c2a",
"client-request-id": "ed77306f-fc7a-42ca-820a-976809140c2a",
"x-ms-ags-diagnostic": "{\"ServerInfo\":{\"DataCenter\":\"West US 3\",\"Slice\":\"E\",\"Ring\":\"2\",\"ScaleUnit\":\"000\",\"RoleInstance\":\"PH1PEPF0001A2F2\"}}",
"x-ms-environment-id": "46a2f7d0-f4f0-e9e8-8f30-55ec3cdd400b",
"x-ms-tenant-id": "72f988bf-86f1-41af-91ab-2d7cd011db47",
"x-ms-dlp-re": "PostMessageToConversation|False",
"x-ms-dlp-gu": "-|-",
"x-ms-dlp-ef": "-|-/-|-|-",
"x-ms-mip-sl": "-|-|-|-",
"Timing-Allow-Origin": "*",
"x-ms-apihub-cached-response": "false",
"x-ms-apihub-obo": "false",
"Date": "Sun, 02 Nov 2025 02:10:15 GMT",
"Content-Type": "application/json",
"Content-Length": "276"
},
"body": {
"error": {
"code": "BadRequest",
"message": "UnknownError",
"innerError": {
"date": "2025-11-02T02:10:15",
"request-id": "ed77306f-fc7a-42ca-820a-976809140c2a",
"client-request-id": "ed77306f-fc7a-42ca-820a-976809140c2a"
}
}
}
}

Expected Behavior

Action should return 2xx and include the message metadata (id, webUrl) when the post succeeds.

Actual Behavior

Action returns 400 UnknownError despite successful post creation.

Environment Details

Environment ID: 46a2f7d0-f4f0-e9e8-8f30-55ec3cdd400b

Tenant ID: 72f988bf-86f1-41af-91ab-2d7cd011db47

Region: West US 3

Request ID: ed77306f-fc7a-42ca-820a-976809140c2a

Timestamp: 2025-11-02T02:10:15

Business Justification

We need reliable metadata for downstream automation:

Linking to the Teams post for audit and traceability.
Updating the original message in future runs.
Current failure forces brittle workarounds (e.g., separate Graph calls, correlation tokens) and violates design principles for deterministic automation.