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ReportSummary
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 = Userlocation = Channel- Parameters:
groupId = 3b51e7d4-b8ba-425e-8b11-be85c83241fachannelId = VoiceApps Deployment Tracker AutomationmessageBody = 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"
}
}
}
}
- Message appears in Teams:
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.
Ask
- Investigate connector pipeline for
PostMessageToConversationwhenposter = User. - Provide ETA for fix or documented workaround that returns message metadata on success.
- Confirm if this is a known issue and whether switching to Graph API is the recommended interim solution.
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