WFM API 429s during schedule import load test

Can anyone clarify the rate limits for WFM schedule imports?

Trying to validate API throughput for bulk schedule updates. Using JMeter 5.6.2 from Singapore to hit POST /api/v2/wfm/schedules/{scheduleId}/imports. Single request works fine. Ramping to 10 concurrent threads triggers immediate 429s.

HTTP/1.1 429 Too Many Requests
Retry-After: 30

The docs mention generic platform limits, but WFM endpoints seem stricter. Is there a specific throttle for import jobs? Or is this a hard cap on concurrent write operations for the schedule resource? Looking to adjust the ramp-up strategy in the script. Current setup uses basic auth token with no caching. Just need to know if 10 threads is realistic or if I need to stagger requests significantly. Any insights on acceptable concurrency for WFM write operations would help tune the test plan.