I’m encountering the same 424 “Failed Dependency” error in the OpenAI Agent Builder when connecting my custom MCP server.
My MCP server responds correctly (handshake/initialize returns 200, list_tools/list_actions returns valid JSON) when tested via direct API calls.
It is publicly reachable, over HTTPS, and the schema matches the documented MCP spec.
However, when Agent Builder invokes the internal endpoint (e.g., /v1/dashboard/responses/mcp/list_actions), it fails with 424 – suggesting the problem lies in Agent Builder’s internal validation or workflow orchestration, not in my server’s implementation.
Some helpful reproduction hints:
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The error appears consistently at the tool-listing / list_actions stage.
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The handshake (
initialize) is successful but the next step fails silently (server may not even receive the request).
I hope the OpenAI team can investigate the internal lifecycle between initialize → list_actions and clarify whether there are undocumented constraints (e.g., naming conventions, response times, header requirements) that could trigger the 424. Any update or workaround would be greatly appreciated.