mcp-sse-transport-mcp-server-using-sse-transport-client-appends-mess-9d548e17

THEN When implementing SSE transport in an MCP client, ensure the client uses the endpoint URL exactly as provided by the server in the /sse response. Do not assume the endpoint is <base>/messages. The client should store and reuse the endpoint for all subsequent requests. As SSE transport is deprecated, consider migrating to the streamable HTTP transport.

// Assume sessionEndpoint is obtained from the /sse response
let sessionEndpoint = await getSessionEndpoint();
// Use sessionEndpoint for all POST requests, not /messages suffix
await fetch(sessionEndpoint, { method: 'POST', body: ... });