### Answer This is a known issue that other users have encountered. Based on community troubleshooting, here are the key requirements to check: [(1) ]() 1. Serve the manifest at the correct path: Your MCP server needs to serve the manifest at

/.well-known/mcp/manifest.json

2. Enable CORS headers for the Retell dashboard:

Access-Control-Allow-Origin: <https://dashboard.retellai.com>
Access-Control-Allow-Methods: GET, POST, OPTIONS
Access-Control-Allow-Headers: Content-Type, Authorization
Access-Control-Allow-Credentials: true

Your server must return

200

to

OPTIONS

preflight requests. 3. Ensure proper response format: - All MCP endpoints must return

Content-Type: application/json

- No redirects, valid JSON (no comments or trailing commas) 4. Debug using DevTools: While the UI says "Loading…", open DevTools → Network and check the request to your domain. If you see CORS/preflight errors, it's the headers; if 200 with wrong type, it's content-type/shape. Required endpoints to verify: -

/.well-known/mcp/manifest.json

→ returns valid JSON -

/mcp/tools

→ returns valid JSON with tool definitions If you've confirmed all of the above and it's still not working, the issue may be on the Retell backend side—some users have reported seeing a

500 Internal Server Error

from

api.retellai.com/get-mcp-tools

in DevTools even when their server is correctly configured.

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

​ To learn more, see the sources I considered: [[1] Мср](https://discord.com/channels/1186424376300679209/1408887968940167168) ​