Severity: High. Blocks testing. Summary MCP server integration works in production phone calls but fails entirely in Retell’s test environment. Chat and simulator sessions never invoke the MCP server, making tool testing impossible before deployment. Environment MCP Server: TypeScript SDK v1.25.1, StreamableHTTP. Retell Agent: Test chat UI and production calls. URL: ngrok to localhost:3000. Auth: Bearer token plus IP whitelist. Behavior Dashboard configuration succeeds. Initialize, SSE, and tools list all work. Production calls invoke tools correctly. Test environment sends zero runtime requests. No sessions. No tools call. Empty server logs. Repro Configure MCP server and verify tools list. Production call triggers tool successfully. Same prompt in test chat never triggers tool. Impact Cannot test or debug MCP tools without live production calls. Forces blind deployment. Request Enable MCP invocation in test environment or document lack of support and provide a workaround.

Hey @duke Retell’s Test Chat environment uses a different execution path than production, often failing to pass the JSON body or failing IP whitelist checks. You can do thing like -Check for Empty Body: -Disable IP Whitelisting for Testing Or Explicit Prompting.