agent does not fill out POST parameters in a custom function Retell AI #❓・ai-evy-support

agent does not fill out POST parameters in a custo...

12/17/2025, 8:52 AM

@AI Evy agent does not fill out POST parameters in a custom function. JSON: { "type": "object", "properties": { "question": { "type": "string", "description": "User's question for the advanced agentic tool, corrected and expanded with any details you think are needed." } } } Agent's tool call: tool_call_id: c236xxxxxxxxx { "question": "What time is it in Sydney?" } Tool Result tool_call_id: c236xxxxxxxxx Axios Error: error code: ERR_BAD_REQUEST, error message: Request failed with status code 429 response status: 429 response data: [{"error":"1","retry_after_seconds":118},"Parameter missing: question."]

AI Evy

12/17/2025, 8:52 AM

Thanks for tagging me @NR. I'll look through relevant sources and get back to you shortly.

AI Evy

12/17/2025, 8:52 AM

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

AI Evy

12/17/2025, 8:52 AM

To learn more, see the sources I considered: [[1] Integrate any system with custom function](https://docs.retellai.com/build/single-multi-prompt/custom-function)

AI Evy

12/17/2025, 8:52 AM

### Answer Based on your tool call output, the agent is correctly filling out the

question

parameter—you can see

{"question": "What time is it in Sydney?"}

in the tool call. [(1) ]() The issue appears to be on the receiving end: 1. The 429 error indicates rate limiting from your external API, not a Retell issue. 2. The "Parameter missing: question" message is coming from your endpoint's response, suggesting your server isn't correctly parsing the request body that Retell sends. How Retell sends custom function requests: For POST requests, Retell sends a JSON body containing: - `name`: the function name - `call`: the call object with context - `args`: the arguments as a JSON object (this is where your

question

parameter lives) Your endpoint needs to extract the parameter from

args

, not from the top level. Example structure Retell sends:

Copy code

json
{
  "name": "your_function_name",
  "call": { ... },
  "args": {
    "question": "What time is it in Sydney?"
  }
}

Troubleshooting steps: 1. Check that your endpoint is reading from

args.question

(or

req.body.args.question

) , not

req.body.question

2. Address the 429 rate limit on your external API 3. Ensure your endpoint URL doesn't have a trailing slash issue (this has caused GET vs POST confusion for others) [(7) ]()

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