What I’ve verified:
- API key was freshly generated from the AI Gateway API Keys page (vck_ prefix)
- Tested both /v1/chat/completions and /v3/ai/language-model endpoints
- Tested multiple models: openai/gpt-4o, openai/gpt-4.1,…
- Same 403 across all models and endpoints — issue is account-level, not model-specific
- Request format is correct (confirmed by getting 400 validation errors before fixing the payload, then 403 once the request was valid)
- An invalid key returns 401 (authentication_error), confirming the key authenticates but access is denied