curl --request POST \
  --url https://{subdomain}.outseta.com/api/v1/attributes/{entityType}/definitions \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "Label": "T-shirt size",
  "ControlType": "Select",
  "ControlParams": "{\"Options\":[\"Small\",\"Medium\",\"Large\"]}"
}
'

import requests

url = "https://{subdomain}.outseta.com/api/v1/attributes/{entityType}/definitions"

payload = {
    "Label": "T-shirt size",
    "ControlType": "Select",
    "ControlParams": "{\"Options\":[\"Small\",\"Medium\",\"Large\"]}"
}
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({
    Label: 'T-shirt size',
    ControlType: 'Select',
    ControlParams: '{"Options":["Small","Medium","Large"]}'
  })
};

fetch('https://{subdomain}.outseta.com/api/v1/attributes/{entityType}/definitions', 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://{subdomain}.outseta.com/api/v1/attributes/{entityType}/definitions",
  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([
    'Label' => 'T-shirt size',
    'ControlType' => 'Select',
    'ControlParams' => '{"Options":["Small","Medium","Large"]}'
  ]),
  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://{subdomain}.outseta.com/api/v1/attributes/{entityType}/definitions"

	payload := strings.NewReader("{\n  \"Label\": \"T-shirt size\",\n  \"ControlType\": \"Select\",\n  \"ControlParams\": \"{\\\"Options\\\":[\\\"Small\\\",\\\"Medium\\\",\\\"Large\\\"]}\"\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://{subdomain}.outseta.com/api/v1/attributes/{entityType}/definitions")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"Label\": \"T-shirt size\",\n  \"ControlType\": \"Select\",\n  \"ControlParams\": \"{\\\"Options\\\":[\\\"Small\\\",\\\"Medium\\\",\\\"Large\\\"]}\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://{subdomain}.outseta.com/api/v1/attributes/{entityType}/definitions")

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  \"Label\": \"T-shirt size\",\n  \"ControlType\": \"Select\",\n  \"ControlParams\": \"{\\\"Options\\\":[\\\"Small\\\",\\\"Medium\\\",\\\"Large\\\"]}\"\n}"

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

{
  "Uid": "string",
  "_objectType": "string",
  "Created": "string",
  "Updated": "string",
  "ActivityEventData": {},
  "ControlType": "string",
  "ControlParams": "string",
  "Label": "string",
  "SystemName": "string",
  "EntityType": 0,
  "Position": 0,
  "Hidden": false
}

{
  "ErrorMessage": "string",
  "EntityValidationErrors": [
    {
      "Entity": {},
      "TypeName": "string",
      "ValidationErrors": []
    }
  ]
}