You have reached your usage limit / billing hard limit reached
You hit the monthly spend cap (the “hard limit”) on your account, so the API stops serving requests until you raise the limit or the month resets. It protects you from runaway bills — but it also stops production traffic dead.
An autonomous agent can burn a month’s budget in a day. Flat-rate removes the cliff entirely.
With a flat monthly price there is no spend cap to slam into and no surprise bill to cap against — usage is unlimited, so production traffic never stops because a budget ran out.
It can — the hard limit is the safety net against runaway usage. Find and fix what spiked first, or move to flat-rate pricing where there’s no per-token meter running.