Voice going silent with inference quota exceeded

We are using the Build plan, which advertises included inference credits.

Billing shows only modest usage (approximately 46k input tokens, 10k output tokens for GPT-4.1 and similar low usage across STT/TTS), and the next invoice is $0.

However, every new Agent session immediately fails with:
HTTP 429
inference_quota_exceeded
LLM token credit quota exhausted

The agent successfully joins the room, receives the configuration, and then fails on the first inference request.
Is there an account issue or another quota that is not reflected on the Billing page?
This was working fine earlier but just failed.