Nixflex - AI Voice Platform for Building AI Phone Agents

Create agent

curl --request POST \
  --url https://api.nixflex.com/v1/agents

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.nixflex.com/v1/agents",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.nixflex.com/v1/agents"

	req, _ := http.NewRequest("POST", url, nil)

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

require 'uri'
require 'net/http'

url = URI("https://api.nixflex.com/v1/agents")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)

response = http.request(request)
puts response.read_body

POST

agents

Create agent

curl --request POST \
  --url https://api.nixflex.com/v1/agents

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.nixflex.com/v1/agents",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.nixflex.com/v1/agents"

	req, _ := http.NewRequest("POST", url, nil)

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

require 'uri'
require 'net/http'

url = URI("https://api.nixflex.com/v1/agents")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)

response = http.request(request)
puts response.read_body

Creates a new AI agent. The agent immediately becomes available to attach to phone numbers and use for outbound calls.

Request

curl -X POST https://api.nixflex.com/v1/agents \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Acme Dental Receptionist",
    "system_prompt": "You are the friendly front-desk assistant at Acme Dental in Croydon...",
    "welcome_message": "Hello, Acme Dental, how can I help?",
    "voice_id": "Ashley",
    "language": "multi",
    "transfer_number": "+442087601234",
    "webhook_url": "https://api.acmedental.com/nixflex/calls"
  }'

Body parameters

Only name is recommended in practice — every other field has a sensible default. You can create a working agent with a one-line payload.

Core

Field	Type	Required	Default	Notes
`name`	string	No	`"Untitled Agent"`	Display name (max 100 chars)
`system_prompt`	string	No	friendly assistant	The AI’s instructions (max 16000 chars, about 4000 tokens)
`welcome_message`	string	No	`"Hello! How can I help you today?"`	First line spoken on inbound calls
`voice_id`	string	No	`"Ashley"`	Voice name. Browse voices in the dashboard
`language`	string	No	`"multi"`	Default language. `multi` follows the caller across English, Spanish, French, German, Italian, Portuguese, Dutch, Hindi, Russian and Japanese. Arabic, Hebrew, Korean, Chinese and Polish need their own code. See Languages
`is_active`	bool	No	`true`	Set false to disable without deleting

Behaviour

Field	Type	Required	Default	Notes
`temperature`	number	No	`0.3`	AI temperature, `0`-`1`
`response_length`	enum	No	`"short"`	`short`, `medium`, `long`
`ai_speaks_first`	bool	No	`true`	Agent greets caller immediately
`dynamic_greeting`	bool	No	`false`	AI improvises greeting per call instead of static welcome
`interruption_sensitivity`	int	No	`50`	`0`-`100`. Lower = harder to interrupt
`response_eagerness`	int	No	`200`	How long the agent waits after the caller stops speaking, in milliseconds. Range `0`-`1000`. Lower is snappier; `0` replies the moment the words are final. Shown as Response Delay in the dashboard	`n	`boosted_keywords`	string	No	`null`	Comma-separated words your callers say that speech recognition might mishear - staff names, treatments, products, place names. Up to 50. Example: `Dr Patel, hygienist, root canal, Meadow Lane`
`pickup_delay`	int	No	`10`	Seconds the agent waits after pickup before speaking. Range 5–30.

Call controls

Field	Type	Required	Default	Notes
`max_call_duration_seconds`	int	No	`600`	Hard cap on call length. Range 60–1800 (1–30 min). See End call.
`silence_hangup_seconds`	int	No	`30`	Hang up if caller silent this long. Range 5–45. See End call.
`record_call`	bool	No	`true`	Save call audio to Supabase Storage. Recordings are deleted after 90 days, and a number can override this. See Call recording.
`amd_enabled`	bool	No	`false`	Ask the carrier to detect an answering machine and hang up about 4 seconds in. Costs extra per answered call on your own carrier bill. With it OFF the agent detects voicemail from the first thing it hears and can leave a message, so ON means a fast hangup and NO message. See Voicemail detection.
`dtmf_enabled`	bool or null	No	`null`	Let callers type digits on their phone keypad instead of saying them. `null` means not set, and a number can override it. See Keypad input.
`webhook_url`	string	No	`null`	Where to POST post-call data

Functions (tools the agent can call mid-conversation)

Field	Type	Required	Default	Notes
`func_end_call`	bool	No	`true`	Agent can end the call cleanly
`transfer_whisper`	string	No	`null`	Warm transfer briefing text. If empty, the AI auto-generates from the conversation.
`func_send_sms`	bool	No	`false`	Not enforced. Accepted and returned, but the engine does not read it, so the agent can text mid-call whichever way this is set. Control it in your prompt - see the note below.
`func_cold_transfer`	bool	No	`false`	Not enforced. Same as above - accepted, returned, and not read. Transfer is controlled by your prompt and by `transfer_number`.
`transfer_type`	enum	No	`"cold"`	`cold` or `warm`. Applies to inbound, outbound, and batch calls made by this agent. See Transfer.
`transfer_number`	string	No	`null`	Default destination for transfers

How to stop the agent texting or transferring. These two are controlled by your prompt, not by a flag. The engine’s own rules tell the model to text only if the developer prompt asks it to, and the same holds for transfers - so a prompt that never mentions texting produces an agent that never texts. func_send_sms and func_cold_transfer are kept because removing a field developers may already send would break them silently, but they have no effect.

A prompt instruction is reliable but not absolute - a language model can still ignore one. If you need a hard guarantee that a number never texts or never transfers, do not rely on the prompt alone. Get in touch: a per-number switch is on the roadmap and is worth building against a real requirement rather than a guess.

Other

Field	Type	Required	Default	Notes
`voice_speed`	number	No	`0.85`	Ignored. Accepted and returned for backwards compatibility, but nothing in the engine reads it. Use `speaking_rate` below.
`speaking_rate`	number or null	No	`null`	How fast the agent talks. `1` is normal, `0.5` is half speed, `1.5` is half again as fast. A value outside that range is clamped to the nearest limit rather than rejected. `null` means normal speed, which is not the same as sending `1`. A number can override this. See Voices.
`greet_by_name`	bool	No	`true`	When a returning caller is recognised, greet them by the name on file (for example, Hi John). Set `false` for a neutral greeting.
`fallback_message`	string	No	”I am sorry, could you say that again?”	Said when transcription fails
`phone_number`	string	No	`null`	Legacy. Numbers are now managed via `/phone-numbers`

Response

201 Created:

{
  "id": "1083c0db-699e-49ee-aa6c-aab29e2d87cf",
  "agent_id": "agent_125207e452f8714a",
  "api_key_id": "nxf_a1b2c3d4...",
  "name": "Acme Dental Receptionist",
  "system_prompt": "You are the friendly front-desk assistant...",
  "welcome_message": "Hello! How can I help you today?",
  "voice_id": "Ashley",
  "language": "multi",
  "temperature": 0.3,
  "response_length": "short",
  "ai_speaks_first": true,
  "dynamic_greeting": false,
  "interruption_sensitivity": 50,
  "pickup_delay": 10,
  "max_call_duration_seconds": 300,
  "silence_hangup_seconds": 10,
  "record_call": true,
  "func_end_call": true,
  "transfer_whisper": null,
  "func_send_sms": false,
  "transfer_type": "cold",
  "transfer_number": null,
  "webhook_url": null,
  "phone_number": null,
  "voice_speed": 0.85,
  "speaking_rate": null,
  "dtmf_enabled": null,
  "amd_enabled": false,
  "greet_by_name": true,
  "transfer_whisper": null,
  "fallback_message": "I am sorry, could you say that again?",
  "is_active": true,
  "created_at": "2026-05-24T01:48:10Z",
  "updated_at": "2026-05-24T01:48:10Z"
}

Save the agent_id — you’ll use it for every subsequent operation.

Next step

Attach a phone number, on Twilio or Telnyx, so the agent can make and receive calls. See Import phone number.

Errors

Code	Cause
`prompt_too_long`	`system_prompt` exceeds 16000 characters
`invalid_voice_id`	Voice not in supported list
`invalid_language`	Language code not supported
`invalid_request`	Missing required field or bad format

See Errors for handling patterns.

API

Platform API

Create agent

Request

Body parameters

Core

Behaviour

Call controls

Functions (tools the agent can call mid-conversation)

Other

Response

Next step

Errors

​Request

​Body parameters

​Core

​Behaviour

​Call controls

​Functions (tools the agent can call mid-conversation)

​Other

​Response

​Next step

​Errors

Request

Body parameters

Core

Behaviour

Call controls

Functions (tools the agent can call mid-conversation)

Other

Response

Next step

Errors