[BUG] Slack MCP "Failed to connect" — cannot reconnect after re-authentication

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?

▎ Issue: Slack MCP "Failed to connect" — cannot reconnect after re-authentication

▎ Error: {"jsonrpc":"2.0","id":null,"error":{"code":-32001,"message":"missing_token"}}

▎ Reference ID: ofid_927339d69f9098ff

▎ Details:
▎ - Other MCP servers (Clockwise, Notion, Gmail, Google Calendar, Miro) all connect successfully
▎ - Slack only returns missing_token after OAuth flow
▎ - Tried: disable/enable, remove/re-add from Claude Desktop, re-authenticate multiple times
▎ - Endpoint https://mcp.slack.com/mcp returns HTTP 401 (reachable)

What Should Happen?

repair

Error Messages/Logs

{"jsonrpc":"2.0","id":null,"error":{"code":-32001,"message":"missing_token"}}

Steps to Reproduce

▎ Details:
▎ - Other MCP servers (Clockwise, Notion, Gmail, Google Calendar, Miro) all connect successfully
▎ - Slack only returns missing_token after OAuth flow
▎ - Tried: disable/enable, remove/re-add from Claude Desktop, re-authenticate multiple times
▎ - Endpoint https://mcp.slack.com/mcp returns HTTP 401 (reachable)

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

latest

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_