This usually happens if you are using a proxy (e.g., Cloudflare or a corporate firewall) and it blocks requests that look like automated agents.
Override the default OpenAI request headers to include a valid User-Agent in ModelAuditor:
extra_kwargs={"default_headers": {"User-Agent": "SimpleAudit-test/1.0"}} # for model calls
# or
judge_extra_kwargs={"default_headers": {"User-Agent": "SimpleAudit-test/1.0"}} # for judge calls