mcp-sse-endpoint-usage-mcp-client-appends-messages-to-the-endpoint-receiv-a6ffe7aa

THEN Ensure the MCP client uses the exact endpoint returned by the /sse endpoint without modification. The server's SSE response includes the full URL for POST messages; the client must not append '/messages' or alter the path. This prevents breakage when the server uses a custom path (e.g., /mcp?sessionId=123).

// Incorrect: client appends '/messages'
const endpoint = sseEndpoint + '/messages';
// Correct: use exact endpoint from /sse response
const endpoint = sseEndpoint;