No session ID found when calling other agents

Hello callin.io community!

I'm encountering a persistent error when trying to use the LangChain Tool Workflow node to call a sub-workflow. I initially had memory-related errors, but now I'm getting a “Referenced node doesn’t exist” error. I'd appreciate some guidance from anyone who has successfully implemented this pattern.

The Error

When executing my workflow, I receive this error:

json

{
  "errorMessage": "Referenced node doesn't exist",
  "errorDetails": {},
  "n8nDetails": {
    "time": "5/21/2025, 5:29:53 PM",
    "n8nVersion": "1.90.2 (Cloud)",
    "binaryDataMode": "filesystem",
    "cause": {
      "executionId": "1602",
      "workflowId": "pYHGkQINJU42w9HS"
    }
  }
}

My Setup

I'm attempting to build an AI agent with LangChain that utilizes tools implemented as sub-workflows. Here's what I've tried so far:

1. First, I set up a main workflow with a Chat Trigger node and a LangChain Tool Workflow node that calls another workflow.
2. Initially, I encountered a “No session ID found” error in the “Simple Memory” node of my sub-workflow, which indicated I needed to pass the session ID to maintain conversation context.
3. I then tried passing {{ $json.sessionId }} in the workflow inputs of my Tool Workflow node, but received a “Key parameter is empty” error.
4. Now, the error has changed to “Referenced node doesn’t exist”.

What I’m Trying to Accomplish

I'm building an AI agent workflow where:

• The main workflow receives user input via a Chat Trigger.
• It processes the input with LangChain (or Claude/GP).
• When specific tasks need to be performed, it calls specialized sub-workflows via the Tool Workflow node.
• These sub-workflows need to maintain memory/context between calls.

Skærmbillede 2025-05-21 214736684×362 12.7 KB