MCP Server trigger

Questions
1

when I create MCP server trigger, I can connect using postman , But I send meesage， it response error 'Invalid message: { “type”: “message”, “message”: “Hello MCP!” } ’

2

Hi there!

That Invalid message error is just MCP’s way of saying, “I was expecting a different JSON format.”

Every request has to be wrapped in a tiny “envelope” called JSON-RPC.
Here’s the minimum it needs:

json

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/list",
  "params": {}
}

If you post something simpler like

json

{ "type":"message", "message":"Hello MCP!" }

MCP doesn’t recognise it and shows the error you saw.

Postmat

  1. URL → the /messages endpoint you see in n8n.
  2. Method → POST.
  3. Header → Content-Type: application/json.
  4. Body → use the JSON-RPC envelope (example above).

Send it and you should get a clean reply instead of the error.

let me know.