Per-region quota limit exceeded

Your app uses a cloud vendor API that enforces a SEPARATE quota per region. At 14:00 a feature degrades for users in one region (eu-west), calls there error at ~60% with 429 'quota exceeded', while the same feature works perfectly for US and APAC users. Dashboards: your GLOBAL call volume to the vendor is well under your overall quota, but the eu-west regional endpoint is pinned at its per-region cap; eu-west traffic grew after a product launch there last week. No code change today. How do you triage and mitigate?