Bad Request of "Missing Session Id" from a stateful MCP server

[jzhouw]

I used the MCP Client SDK and was trying to call a MCP server. With a test connection of calling the ListServerTools and got below response:

Response status code does not indicate success: 400 (Bad Request). Response body: {"jsonrpc":"2.0","id":"server-error","error":{"code":-32600,"message":"Bad Request: Missing session ID"}}

I have read the document here https://csharp.sdk.modelcontextprotocol.io/v1/concepts/stateless/stateless.html

In my understanding the client SDK should be able to handle the Mcp_Session_Id internally, or anything I have missed?

[jeffhandley]

@jzhouw Can you share you repro please?

[jzhouw]

var transport = new HttpClientTransport(new HttpClientTransportOptions
{
    Endpoint = new Uri(url),
    TransportMode = HttpTransportMode.Sse,
    MaxReconnectionAttempts = 5,
    DefaultReconnectionInterval = TimeSpan.FromSeconds(1),
    AdditionalHeaders = new Dictionary<string, string> { { "Authorization", $"Bearer {key}" } }
});
var mcpClient = await McpClient.CreateAsync(transport);
var serverTools = await mcpClient.ListToolsAsync();

it's very basic test code above. I don't have access to the MCP server source