Regional provider degradation

Your payment provider is 'up' globally per their status page, but starting 17:00 your checkout success rate drops, yet only for customers in one region (APAC), from 96% to 70%, while EU and US checkout is totally normal. Dashboards: calls to the provider succeed quickly for US/EU; for APAC, ~30% time out or return 5xx and the rest are slow. The provider says they see 'no global incident.' You route all payment calls through the provider's single global endpoint. No deploy. How do you triage and mitigate?