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HTTP status

400 invalid_request_error

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Typical cause

The model is only served via the Response API — OpenAI pro-tier models such as gpt-5.5-pro — and the request uses /v1/chat/completions or /v1/messages. /v1/messages returns this error in the Anthropic error envelope, which carries the same message and suggestion but no code field.

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Resolution

Call POST /v1/responses with a Response API body (input, not messages): 
curl https://api.auriko.ai/v1/responses \
  -H "Authorization: Bearer $AURIKO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "gpt-5.5-pro", "input": "Hello"}'
To check endpoint support before sending, read supported_endpoints from GET /v1/models?endpoint=responses or from each provider entry in the model directory. If your integration only speaks Chat Completions, choose a chat-capable model instead.