---
title: OpenAI 400 Error
description: "How to debug OpenAI 400 errors in Hermes Agent, including malformed requests, model assumptions, and payload issues."
canonical: "https://deploy-hermes.com/troubleshooting/openai-400-error"
last-updated: "2026-08-23"
---

# OpenAI 400 Error

> How to debug OpenAI 400 errors in Hermes Agent, including malformed requests, model assumptions, and payload issues.

Canonical: https://deploy-hermes.com/troubleshooting/openai-400-error
Updated: 2026-08-23 · Search intent: troubleshooting
Category: [Troubleshooting](/troubleshooting)

OpenAI 400 errors usually mean the request made it to the provider but something about the payload or model selection is invalid.

## What the symptom usually means

You see the runtime contact OpenAI, but the provider rejects the request immediately instead of timing out or failing authentication.

## Most likely causes

Likely causes include unsupported model names, malformed payload fields, overlarge request bodies, or mixing settings that the selected endpoint does not accept.

## Recommended fix order

Capture the failing request context, confirm the model and endpoint are compatible, shrink the payload if needed, and rerun a minimal request before restoring complexity.

Work from identity and connectivity first, then provider settings, then higher-level prompt or runtime assumptions. That sequence avoids wasting time on downstream symptoms.

## Frequently asked questions

### Does a 400 mean my API key is wrong?

Usually no. Wrong keys more often produce authentication failures, while 400s point to request shape problems.

### What should I trim first?

Start with context size, optional fields, and any model-specific parameters you are not sure the endpoint accepts.

---

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