429 rate limited

{"ok": false, "error": "Rate limit: 30 submits per minute.", "retryAfterSeconds": 41}

Buckets are per account, fixed one-minute windows: submit 30, quote 60, verify 10, staging 20, draft 30, campaign 20, cancel 30. Back off for retryAfterSeconds (also in the retry-after header). Parallel workers share the account's bucket; serialise submits or batch rows into fewer, larger calls (inline up to 10,000 rows; staged up to 250,000).