n8n not connecting

[left-society]

MCP server URL

https://vibeacademy.cloud/mcp-server/http

Where does the issue occur?

When auth finishes and redirects back to Claude.ai

Transport used

streamable-http

Client registration type

Dynamic Client Registration (DCR)

SSE only: Does your server return the expected status code for POST requests?

Not applicable (my server does not use SSE)

When did you last reproduce this?

2026-04-03 ~10:00 AM UTC

Browser and OS

Chrome on macOS (Tahoe)

Describe the issue

When attempting to add the n8n Instance-level MCP server (https://vibeacademy.cloud/mcp-server/http) as a custom connector in Claude.ai, the connection fails with the errors "A server with this URL already exists" and "Failed to add connector". The n8n MCP server is enabled and has previously connected Claude clients (shown in the Connected clients tab), but Claude.ai refuses to connect or reconnect, displaying these errors after the OAuth auth flow completes and redirects back to Claude.ai.

Issue details

Two error banners appear in Claude.ai after attempting to add the custom connector:
1. "A server with this URL already exists."
2. "Failed to add connector"

Steps to reproduce:
1. Go to Claude.ai > Customize > Connectors
2. Click "+" to add a custom connector
3. Enter name "n8n" and URL "https://vibeacademy.cloud/mcp-server/http"
4. Click "Add"
5. The errors appear immediately — both "A server with this URL already exists." and "Failed to add connector" are shown as warning banners

The n8n Instance-level MCP is enabled (v2.14.2) and the server URL is https://vibeacademy.cloud/mcp-server/http. The n8n dashboard shows two existing "Claude" clients previously connected (13 and 19 minutes ago), suggesting OAuth was completed before but the connection is not functional on Claude.ai's side.

Expected behavior

After completing the OAuth authentication flow, Claude.ai should successfully connect to the n8n MCP server and display it as an active connector in the Connectors list. The n8n MCP server's tools and workflows should then be available for use within Claude.ai conversations.

Logs from your server

Additional context

n8n version: 2.14.2. n8n Instance-level MCP is enabled with OAuth support (shows OAuth and Access token tabs in connection details). Server URL: https://vibeacademy.cloud/mcp-server/http. The n8n Connected clients tab shows 2 previously connected "Claude" clients (13 min ago and 19 min ago), indicating OAuth was initiated before but connection is not completing on Claude.ai's side. The "n8n" connector appears in Claude.ai's "Not connected" section, suggesting it was added previously but is no longer functional. Both errors appear simultaneously: "A server with this URL already exists." and "Failed to add connector".

[localden]

Thanks for the report. We looked at how n8n connections behave in aggregate and the most common failure modes are configuration-related rather than a Claude-side bug:

• Workspace URL typo or inactive workspace. Double check that your https://<workspace>.app.n8n.cloud URL is correct and the workspace is active.
• MCP access disabled in the workspace. n8n has a per-workspace setting that controls whether MCP clients can connect. Make sure it is enabled.
• Self-hosted n8n on a private network. Claude can only reach servers on the public internet. Servers on private IPs, internal hostnames, or behind a firewall that blocks Claude's published IP range will not connect.

There is also a smaller share of intermittent server-side errors from n8n itself that we are following up on with them separately.

If you have checked the above and it still fails, please open a new issue with a fresh request ID from the connector error dialog and we will dig in.