Nixflex - AI Voice Platform for Building AI Phone Agents

Send SMS

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

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.nixflex.com/v1/sms",
  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/sms"

	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/sms")

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

sms

Send SMS

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

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.nixflex.com/v1/sms",
  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/sms"

	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/sms")

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

Sends a single SMS from one of your imported numbers. Works on Twilio and Telnyx. Useful for one-off messages, status updates, or reminders that do not need a phone call.

This endpoint uses to for the recipient. The outbound-call endpoint (POST /v1/calls/outbound) uses to_number instead. They are different field names for the same idea - sending to_number here will fail with a missing-field error. Double-check when copying between the two.

Request

curl -X POST https://api.nixflex.com/v1/sms \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET" \
  -H "Content-Type: application/json" \
  -d '{
    "agent_id": "agent_125207e452f8714a",
    "to": "+447386172392",
    "from_number": "+447446466847",
    "message": "Reminder: your appointment is tomorrow at 2pm. Reply YES to confirm."
  }'

Body parameters

Field	Type	Required	Notes
`agent_id`	string	Yes	Agent that owns this SMS - its `system_prompt` handles any replies
`to`	string	Yes	Recipient in E.164 (this endpoint uses `to`, not `to_number`)
`message`	string	Yes	Message text. 600 chars recommended for reliable carrier delivery. Carrier hard caps are typically 1600. See SMS length guide.
`from_number`	string	No	Which of your imported numbers to send from, on either carrier. If omitted, the agent’s own number is used. Required only if the agent has no number of its own.
`context`	object	No	Optional reply context. Pass `{ "reply_context": "..." }` to give the agent extra background for handling replies to this specific message.

Response

201 Created:

{
  "status": "sent",
  "to": "+447386172392",
  "from": "+447446466847"
}

Status updates come asynchronously via your carrier’s status callbacks. Telnyx does not report delivery status yet, so a message sent from a Telnyx number stays at sent. Final status (delivered, failed, undelivered) reflects in the message record within ~30 seconds.

Reply behaviour

If the recipient replies, the agent automatically answers using its system_prompt. There is no separate reply-handling system. For per-message context, pass a context object with reply_context - the agent uses it when answering replies to that message. Otherwise, put any standing context the agent needs directly in its system_prompt before sending. See Send SMS concept page for details.

Errors

HTTP	Error message	Cause
400	`Required: agent_id, to, message`	One of the required fields is missing
404	`Agent not found`	`agent_id` does not exist or is not yours
400	`from_number required - this agent has no number of its own, so specify which imported number to send from`	No `from_number` passed and the agent has no number
400	(credentials error)	The chosen number has no carrier credentials stored
500	`Failed to send SMS via Twilio`	Twilio rejected the send

API

Platform API

Send SMS

Request

Body parameters

Response

Reply behaviour

Errors

​Request

​Body parameters

​Response

​Reply behaviour

​Errors

Request

Body parameters

Response

Reply behaviour

Errors