Digital Messaging Webhook 429s at low concurrency

Can anyone clarify why POST /api/v2/communications/messages/webhooks returns 429 Too Many Requests when JMeter 5.6.2 hits just 20 concurrent threads? Testing from Asia/Singapore against BYOC Edge 24.2.

Environment details:

  • Tool: JMeter 5.6.2
  • Region: Asia/Pacific Southeast
  • Endpoint: /api/v2/communications/messages/webhooks
  • Threads: 20 concurrent