invalid-mcp-message

Status	400
Title	Invalid MCP message
Code	invalid-mcp-message
Type	https://docs.satellitedata.net/problems/invalid-mcp-message

Coming later This problem belongs to the MCP endpoint, which lean v1 does not have yet.

Meaning

A message to POST /mcp is not valid JSON-RPC 2.0 for the Model Context Protocol transport.

Likely causes

• A missing Mcp-Session-Id header after initialize.
• A body that is not a JSON-RPC request or notification.

Fix

Call initialize first and repeat the returned Mcp-Session-Id on every later request.

Example

The detail is the example from the v1 contract.

{
  "type": "https://docs.satellitedata.net/problems/invalid-mcp-message",
  "title": "Invalid MCP message",
  "status": 400,
  "detail": "Mcp-Session-Id is required after initialize.",
  "instance": "/v1/...",
  "code": "invalid-mcp-message",
  "requestId": "01JQ7Z3M8R5V2W6X9Y0A1B2C3D"
}

See Errors for the members every problem carries.