curl --request POST \
  --url https://app.lettr.com/api/audience/segments \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "name": "Engaged subscribers",
  "conditions": {
    "groups": [
      {
        "conditions": [
          {
            "field": "email",
            "operator": "equals",
            "value": "@example.com"
          }
        ]
      }
    ]
  },
  "list_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
}
'

import requests

url = "https://app.lettr.com/api/audience/segments"

payload = {
    "name": "Engaged subscribers",
    "conditions": { "groups": [{ "conditions": [
                    {
                        "field": "email",
                        "operator": "equals",
                        "value": "@example.com"
                    }
                ] }] },
    "list_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    name: 'Engaged subscribers',
    conditions: {
      groups: [{conditions: [{field: 'email', operator: 'equals', value: '@example.com'}]}]
    },
    list_id: '3c90c3cc-0d44-4b50-8888-8dd25736052a'
  })
};

fetch('https://app.lettr.com/api/audience/segments', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://app.lettr.com/api/audience/segments",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'name' => 'Engaged subscribers',
    'conditions' => [
        'groups' => [
                [
                                'conditions' => [
                                                                [
                                                                                                                                'field' => 'email',
                                                                                                                                'operator' => 'equals',
                                                                                                                                'value' => '@example.com'
                                                                ]
                                ]
                ]
        ]
    ],
    'list_id' => '3c90c3cc-0d44-4b50-8888-8dd25736052a'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json"
  ],
]);

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

curl_close($curl);

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

package main

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

func main() {

	url := "https://app.lettr.com/api/audience/segments"

	payload := strings.NewReader("{\n  \"name\": \"Engaged subscribers\",\n  \"conditions\": {\n    \"groups\": [\n      {\n        \"conditions\": [\n          {\n            \"field\": \"email\",\n            \"operator\": \"equals\",\n            \"value\": \"@example.com\"\n          }\n        ]\n      }\n    ]\n  },\n  \"list_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n}")

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

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Content-Type", "application/json")

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

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

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://app.lettr.com/api/audience/segments")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"name\": \"Engaged subscribers\",\n  \"conditions\": {\n    \"groups\": [\n      {\n        \"conditions\": [\n          {\n            \"field\": \"email\",\n            \"operator\": \"equals\",\n            \"value\": \"@example.com\"\n          }\n        ]\n      }\n    ]\n  },\n  \"list_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://app.lettr.com/api/audience/segments")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"name\": \"Engaged subscribers\",\n  \"conditions\": {\n    \"groups\": [\n      {\n        \"conditions\": [\n          {\n            \"field\": \"email\",\n            \"operator\": \"equals\",\n            \"value\": \"@example.com\"\n          }\n        ]\n      }\n    ]\n  },\n  \"list_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n}"

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