n8n-io/n8n · error

No sessionId provided

Error message

No sessionId provided

What it means

Fires in McpServer.handleDeleteRequest when an MCP client sends a DELETE request without a session id, so the server cannot identify which streamable-HTTP session to terminate. It is a transport-level guard: the handler rejects the request (responding with an error instead of closing a session) because the MCP streamable HTTP protocol requires the mcp-session-id header/value on deletion requests.

Solutions

1. Send the mcp-session-id returned by the initialize response with the DELETE
2. Use the session termination flow of a compliant MCP client

When it happens

Trigger: Thrown at packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpServer.ts:260 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/654e158cc297bfd8. Report an issue: GitHub.

Appendix: source

Thrown at packages/@n8n/nodes-langchain/nodes/mcp/McpTrigger/McpServer.ts:260

		resp.flush?.();

		// A not-ready gate makes the CallTool handler short-circuit (returning the
		// actionable response over the transport instead of executing). Report it as
		// not a tool call so the node does not also trigger a workflow execution.
		const wasGated = !!gateResult && !gateResult.readyToExecute;

		return {
			wasToolCall: MessageParser.isToolCall(rawBody) && !wasGated,
			toolCallInfo,
			messageId,
		};
	}

	async handleDeleteRequest(req: express.Request, resp: CompressionResponse): Promise<void> {
		const sessionId = this.getSessionId(req);

		if (!sessionId) {
			resp.status(400).send('No sessionId provided');
			return;
		}

		const transport = this.sessionManager.getTransport(sessionId);

		if (transport) {
			this.pendingCallsManager.cleanupBySessionId(sessionId);

			if (transport instanceof StreamableHttpTransport) {
				await transport.handleRequest(req, resp);
				return;
			}
			resp.status(405).send('Method Not Allowed');
			return;
		}

		resp.status(404).send('Session not found');
	}

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