Supabase MCP plugin OAuth fails with "Unrecognized client_id"

Environment

• Claude Code version: 2.1.247
• Plugin: supabase@supabase-community-supabase-plugin v0.1.15 (MCP server: https://mcp.supabase.com/mcp)

Steps to reproduce

1. Install the Supabase plugin via the plugin marketplace.
2. Run /mcp and select the Supabase server to authorize.
3. Complete the OAuth flow in the browser.

Expected behavior
OAuth completes and the MCP server shows as Connected.

Actual behavior
The browser shows:

{"message":"Unrecognized client_id"}

instead of completing the OAuth authorization.

Troubleshooting already tried

• Disabled a duplicate supabase@claude-plugins-official plugin in case of a conflicting registration — no change.
• Disabled/re-enabled the supabase-community-supabase-plugin to force a fresh MCP registration — no change.
• Retried in a completely fresh claude CLI session/process — same error persists.

This suggests the issue is not local/client-side caching but likely a bug in the plugin's OAuth client registration or on the Supabase MCP OAuth server side.