Question

Your service calls a third-party payments provider whose API allows 100 requests/second across your whole account. You autoscaled your worker fleet to clear a backlog, and now a growing fraction of provider calls return HTTP 429 with `Retry-After`. The more workers you add, the higher the 429 rate climbs and the slower the backlog drains. Your own infra is healthy — CPU, memory, and queues on your side are fine. Dashboards show provider 429s rising in lockstep with your worker count. How do you triage and mitigate?