> ## Documentation Index
> Fetch the complete documentation index at: https://docs.viviai.cc/llms.txt
> Use this file to discover all available pages before exploring further.

# Why am I getting 400 or an unsupported parameter error?

Start with the minimal request in the documentation and check the required fields for your protocol:

* **OpenAI Chat:** Uses `messages`.
* **Gemini:** Uses `contents`.
* **Anthropic:** Requires `max_tokens`.

Support for optional sampling, thinking, and multimodal parameters varies by model.

Request parameters: [OpenAI Chat](https://docs.viviai.cc/en/openai-chat.md) · [Gemini](https://docs.viviai.cc/en/gemini.md) · [Anthropic](https://docs.viviai.cc/en/anthropic.md)


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