OAuth failure - "does not support dynamic client registration"

Environment

Plan: Slack Enterprise
Claude Code version: Latest, native install
OS: macOS 26.3.1

Setup

• Installed Slack plugin from the official Anthropic plugin marketplace in Claude Code via /plugin > Discover
• Other MCP connectors work fine in Claude Code

Steps to Reproduce

• Install Claude Code Slack Plugin
• Start Claude Code
• Run /mcp
• Select "Authenticate" from the menu
• No browser window opens
• An error message is displayed

/mcp Output

Plugin:slack:slack MCP Server
Status: ❌ failed
Auth: ❌ not authenticated
URL: https://mcp.slack.com/mcp
Config location: Dynamically configured

Error: Incompatible auth server: does not support dynamic client registration

Possible Issue

The MCP OAuth server metadata returned from the discovery endpoint at https://mcp.slack.com/.well-known/oauth-authorization-server reports an issuer "https://slack.com" which mismatches the expected issuer "https://mcp.slack.com" used to perform the discovery.

The OAuth authorization server metadata at https://mcp.slack.com/.well-known/oauth-authorization-server must contain an issuer field exactly equal to the discovery issuer URI:

{
  ...
  "issuer": "https://mcp.slack.com",
  ...
}

Related Issues

• https://github.com/anthropics/claude-code/issues/18009

Start with the Claude Code /mcp authentication flow and inspect the OAuth discovery response at https://mcp.slack.com/.well-known/oauth-authorization-server. Confirm whether the issuer and dynamic client registration metadata prevent authentication; done means selecting Authenticate opens the browser and the Slack MCP server reports authenticated.