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Nixflex applies rate limits to protect the platform and ensure fair use. Most applications stay well under these limits, but if you’re building high-volume integrations, plan around them.

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API request limits

Per API key:
Endpoint groupLimit
Read operations (GET)600 requests per minute
Write operations (POST, PUT, PATCH, DELETE)120 requests per minute
Authentication endpoints (POST /v1/keys)10 requests per hour
Headers on every response tell you where you stand: 
X-RateLimit-Limit: 600
X-RateLimit-Remaining: 587
X-RateLimit-Reset: 1715900060
X-RateLimit-Reset is a Unix timestamp when the window resets.

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When you hit the limit

You get a 429 response: 
{
  "error": {
    "type": "rate_limit_error",
    "code": "rate_limit_exceeded",
    "message": "Rate limit exceeded. Try again in 12 seconds.",
    "details": {
      "retry_after": 12
    }
  }
}
retry_after tells you how long to wait. Honour it.

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Concurrent call limits

The number of calls running simultaneously per account:
TierConcurrent calls
Pay-as-you-go10
Starter25
Scale100
EnterpriseCustom
If you trigger more outbound calls than your concurrency limit allows, they queue automatically. Inbound calls beyond the limit hear a busy signal. To raise your concurrent call limit, contact support@nixflex.com.

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Batch campaign concurrency

Within a batch campaign, the engine launches calls in waves up to your account’s concurrent call limit. A 1,000-recipient campaign on a 25-concurrent plan takes roughly the average call duration × (1,000 / 25) to complete. You can also throttle a campaign deliberately: 
{
  "agent_id": "agent_xxx",
  "recipients": [...],
  "max_concurrent": 5
}
Useful when you want to keep some headroom for inbound calls.

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SMS rate limits

SMS is rate-limited by Twilio, not Nixflex. Default: 1 message per second per sending number. For high-volume SMS:
  • Add multiple sending numbers (the engine round-robins them)
  • Request a higher Twilio MPS limit from Twilio support
  • Use SMS campaigns, which respect Twilio’s pacing automatically

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Webhook delivery limits

Webhooks fire as fast as your endpoint can accept them, with no Nixflex-side throttle. If your server is slow:
  • Receive the webhook quickly (return 2xx immediately)
  • Process the data in a background queue
  • Don’t do heavy work inside the webhook handler

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When you need more

If you’re running into limits regularly, that’s a signal you’ve outgrown the default tier. Email support@nixflex.com and we’ll raise your limits or move you to a custom plan.