[BUG] Failed to authenticate. API Error: 403 {"error":{"type":"forbidden","message":"Request not allowed"}}

Preflight Checklist

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

What's Wrong?

When attempting to use Google Calendar through Cowork, the task fails with a 403 authentication error. The same Google Calendar connector works correctly in claude.ai in the same account.
Error message:
Failed to authenticate. API Error: 403 {"error":{"type":"forbidden","message":"Request not allowed"}}
Steps to reproduce:

Connect Google Calendar via claude.ai Settings → Connected apps
Open Cowork and assign a task that requires Google Calendar access (e.g. "Review my calendar and show me a summary")
Task fails with the 403 error above

Expected behavior: Cowork should use the same Google Calendar connector/auth as claude.ai
Actual behavior: Cowork returns a 403 forbidden error every time
Troubleshooting already attempted:

Disconnected and reconnected Google Calendar
Fully quit and relaunched Cowork
Reinstalled Cowork
Confirmed the connector works in claude.ai (successfully lists calendars and events)

Environment:

macOS (Tahoe 26.3)
Cowork (Claude 1.1.4173 (12766c) 2026-02-24T15:04:14.000Z)

What Should Happen?

Can't use the CoWork, was returned by

"Failed to authenticate. API Error: 403 {"error":{"type":"forbidden","message":"Request not allowed"}}"

Error Messages/Logs

Steps to Reproduce

1. Open Claude Desktop Mac
2. Switch to Claude CoWork tab
3. Type "Hello" in the chatbox
4. error occurs

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.56 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_