Billing / quota errors across LLM providers

How billing / quota errors show up across Gemini, OpenAI, Anthropic, OpenRouter and more, and how to route around them.

Billing and quota errors mean the credential works but the account behind it can't pay for the call — an exhausted balance, an expired card, or a hard spending cap. Unlike rate limits they don't clear on their own; requests keep failing until someone tops up the account or lifts the cap. Automatic fallback to a second provider keeps agents alive while you fix the account.