You added your Linkilo MCP endpoint to claude.ai (or ChatGPT), clicked Connect, and got:
“Couldn’t register with the plugin’s sign-in service. You can try again, or add an OAuth Client ID in the connector settings.”
This error means the AI app couldn’t complete the automatic sign-in discovery with your site. It’s almost always one of the three causes below — check them in this order.
Cause 1 — MCP access is turned off
MCP is off by default in Linkilo. Go to Linkilo → Manage → MCP Access, tick Enable MCP access, click Save, then delete the connector in the AI app and add it again. While the switch is off, the endpoint refuses every request, and the sign-in screen itself tells you “MCP access is turned off.”
Cause 2 — You’re on Linkilo 2.8 or older
The sign-in (OAuth) flow that web connectors require shipped in Linkilo 2.9 and is included in every later version, including 3.0. Update the plugin, then retry.
Cause 3 — Your host blocks the discovery URLs (nginx and “.well-known”)
Web connectors look up your site’s sign-in details at URLs containing /.well-known/. On some managed hosts running nginx (BigScoots, Kinsta, and similar), the server answers those URLs itself with a 404 — WordPress never runs, so the lookup fails no matter what the plugin does.
The fix is a one-line change only your host can make. Send them this:
A plugin on my site serves OAuth discovery endpoints, but nginx currently returns 404 for URLs containing
/.well-knownbefore WordPress can handle them. Please make these fall through to WordPress (try_files $uri /index.php?$args):/.well-known/oauth-authorization-server*,/.well-known/oauth-protected-resource*, and/wp-json/*/.well-known/*. These are OAuth metadata URLs (RFC 8414/9728) served dynamically by the plugin.
After the host confirms, delete the connector in the AI app, re-add the URL, and Connect again. (Apache hosts don’t have this problem — WordPress handles those URLs out of the box.)
Things that are NOT the cause
- Pasting a token into the URL. Web connectors never use a token — paste only the endpoint URL, exactly as shown on the MCP Access page, and leave the OAuth Client ID/Secret fields empty.
- Wordfence or other security plugins — they don’t block this flow; the sign-in traffic goes through the normal WordPress REST API.
- Your AI provider key. MCP never uses the OpenAI or other provider key saved in AI Settings, so a missing or expired key cannot cause this error.
Need it working right now?
Claude Code and other desktop clients skip discovery entirely and connect with a token immediately — see How to Connect Claude Code and Desktop MCP Clients with a Token.
Last reviewed for Linkilo 3.0.0 (October 2026).