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Nixflex keeps things simple: there is no per-minute request limit on the API. The limits that matter are about how many calls run at the same time (concurrency), and the natural pacing of SMS and webhooks.
Most projects never come close to these limits. If you are planning a high-volume launch, tell us in advance at support@nixflex.com and we will raise your concurrency before you need it.

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Concurrent calls

Concurrency is the number of calls happening at the same moment, not per day. By default your account can run up to 10 concurrent calls, and this can be raised to 50 on request. If you need more than 50, we will size it with you.
1

Outbound calls queue when the limit is reached

If you trigger more outbound calls than your concurrency allows, the extra calls wait in a queue and dial automatically as slots free up. Nothing is dropped.
2

Inbound calls get a busy signal at the limit

Your limit is a single pool shared by inbound and outbound calls. If an inbound call arrives while you are at your limit, the caller gets a busy signal. The call is never answered, so you are not billed for it and it does not appear in your call history.
3

You can see when this happens

The API Keys page in the dashboard shows your peak concurrent calls this month, and warns you if any calls were turned away. If you see that warning, it is time to raise your limit.
4

Raising your limit

Email support@nixflex.com with the concurrency you need and we will raise it.

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Batch campaign concurrency

A batch campaign does not need its own throttle. Every recipient is queued, and calls dial only as slots free up under your account’s concurrency limit. A large campaign simply takes longer to work through - it never overloads your account. Because inbound and outbound share the same limit, a large campaign can use up slots an inbound caller would otherwise get. If you run big campaigns and take inbound calls on the same key, ask us to raise your limit.

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SMS pacing

SMS is paced by your carrier, not by Nixflex. The usual default is about one message per second per sending number. For higher volume:
  • Add more sending numbers so messages spread across them.
  • Ask your carrier to raise your per-number throughput.
  • Use SMS campaigns, which respect your carrier’s pacing automatically.

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Webhook delivery

Webhooks fire as fast as your endpoint can accept them, with no Nixflex-side throttle. To keep up:
  • Return a 2xx response quickly.
  • Do the heavy work in a background queue, not inside the webhook handler.

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Need more?

If you are regularly close to your concurrency, that is a good problem - email support@nixflex.com and we will raise your limit.