[BUG] M365 Connector not working ofid_2dcab06b920d5330

[corbant1]

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

Cannot connect to M365 claude connector, im using latest version of claude, ive granted admin permissions in entra for server + client

What Should Happen?

Connects to M365 connector

Error Messages/Logs

ofid_2dcab06b920d5330

Steps to Reproduce

Connect to M365 connector

Claude Model

None

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

v2.1.80.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

Ive enabled connectors for our organisation, and granted admin perms for the claude server and client 365 in entra, so its not a permissions issue.

[github-actions]

Found 3 possible duplicate issues:

1. [BUG] MS365 plugin OAuth authorization fails with two separate errors #25246
2. [BUG] M365 MCP OAuth fails with AADSTS9000411 - parameter 'prompt' is duplicated #31089
3. [BUG] Microsoft 365 MCP Server authentication fails with AADSTS9000411: duplicated 'prompt' parameter #21309

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
• To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

[github-actions]

Closing for now — this doesn't appear to be about Claude Code. Please open a new issue if this is still relevant.

[McLuck]

This issue looks very similar to a problem I'm currently investigating.

I've opened a new issue with additional context and reproducible details: #41016

If you're experiencing the same behavior (M365 connector / MCP / OAuth issues), it may be helpful to continue the discussion there to consolidate findings.

[corbant1]

Update on this - another user (McLuck) experiencing the same issue did a HAR capture and identified the root cause. For affected users, Claude's backend is sending a POST request to the MCP stream endpoint instead of GET, which returns a 405 Method Not Allowed: Expected: GET /v1/toolbox/shttp/mcp/{id} Actual: POST /v1/toolbox/shttp/mcp/{id} → 405 The CORS preflight only allows GET and OPTIONS, so the connection fails. This is user-specific - other users on the same tenant/org connect fine using the correct GET method. Full writeup with HAR analysis and reproduction steps: #41016 This looks like a feature flag or backend routing inconsistency affecting specific user accounts. My reference IDs: ofid_ff4d4721fdd8f310 and ofid_2dcab06b920d5330. Ng? Mihi | Kind regards, Corban Turley +64 224697146<tel:+64%20224697146> <tel:> [cid:ldelogogoldmed3_bc905204-963b-4be0-9595-2098cbb01f81.png] <https://www.lde.co.nz> LDE Ltd 3a Newhaven Terrace Mairangi Bay, 0630 lde.co.nz<https://lde.co.nz> Geotechnical ? Civil ? Structural ? Environmental Terms<https://lde.co.nz/standard-conditions-of-engagement/> Engineering advice not to be relied on by third parties From: Lucas Israel ***@***.***> Sent: Tuesday, 31 March 2026 4:21 am To: anthropics/claude-code ***@***.***> Cc: Corban Turley ***@***.***>; Author ***@***.***> Subject: Re: [anthropics/claude-code] [BUG] M365 Connector not working ofid_2dcab06b920d5330 (Issue #37969) [https://avatars.githubusercontent.com/u/857454?s=20&v=4]McLuck left a comment (anthropics/claude-code#37969)<#37969 (comment)> This issue looks very similar to a problem I'm currently investigating. I've opened a new issue with additional context and reproducible details: #41016<#41016> If you're experiencing the same behavior (M365 connector / MCP / OAuth issues), it may be helpful to continue the discussion there to consolidate findings. - Reply to this email directly, view it on GitHub<#37969?email_source=notifications&email_token=BMUUWPJP5ZWND7XCMP2OEKD4TKGEJA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIMJVGU4DOMZRGQZ2M4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2KYZTPN52GK4S7MNWGSY3L#issuecomment-4155873143>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/BMUUWPMYKRDAOEMCX7B3X3L4TKGEJAVCNFSM6AAAAACW4TQ2YCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DCNJVHA3TGMJUGM>. You are receiving this because you authored the thread.Message ID: ***@***.******@***.***>>

[arnolduspistorius]

Experiencing the same issue. Microsoft 365 connector has never successfully connected.
Environment:

Claude Team plan, Cowork desktop app
Microsoft 365 tenant with Global Administrator role
Admin consent granted on both M365 MCP Client and Server apps in Entra
Assignment required = No

Diagnostic evidence:

Microsoft Entra sign-in logs show SUCCESS for every auth attempt
Failure occurs after Microsoft issues the token — Anthropic's token exchange rejects or drops it
Tested across Safari, Chrome, Chrome Incognito, and Edge

Error references: ofid_a07545ceda979cd6, ofid_ed9442bd5e67f671, ofid_069dbd005d605c2d
Org ID: be78a289-8718-441e-a890-00c5882be9d9
Support ticket open since 27 March 2026. Only Fin AI responses — no human agent has acknowledged the issue despite multiple escalation requests. This is blocking a $7,000 Microsoft integration.

Please help.

Kind regards,
Arnold

[github-actions]

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.