Issue with custom MCP server

[ksawaray]

Hi there,

I'm encountering an issue when trying to use a custom MCP server created with fastMCP for tool calls via client.responses.create().

• OpenAI version: 1.82.1
• Python version: 3.11.10

from openai import OpenAI

openai_api_key = os.getenv("OPENAI_API_KEY")
client = OpenAI(api_key=openai_api_key)

messages = [{"role": "user", "content": "xxxxxxx"}]

tools = [
        {
            "type": "mcp",
            "server_label": "<server label>",
            "server_url": "http://<my domain>:<port>/mcp",
            "require_approval": "never",
        }
]

response = client.responses.create(
        model="gpt-4o",
        input=messages,
        tools=tools
)

When I execute the code, I get the following error.

openai.APIStatusError: Error code: 424 - {'error': {'message': "Error retrieving tool list from MCP server: 'xxxxxxx'. Http status code: 424 (Failed Dependency)", 'type': 'external_connector_error', 'param': 'tools', 'code': 'http_error'}}

• I confirmed that the URL http://:/mcp is publicly accessible.
• When I changed the tool type to "deepwiki" specified in the official documentation (https://platform.openai.com/docs/guides/tools-remote-mcp), it worked correctly.

Could you please help me understand the root cause of this 424 Failed Dependency error when using a custom MCP server, and how to resolve it?
(Is the issue perhaps related to this library sending requests to https://api.openai.com/v1/responses?)